Verdict up front: a 150m² flat with poor call quality needs a Band 8 900MHz voice booster with at least 60dB gain and 150m² coverage, and the G150 Mobile Booster at £85.00 is the best value solution on the UK market. It delivers 60dB of gain, a 5dBi omnidirectional outdoor antenna, a 5m coaxial cable and a built-in indoor antenna, covering the entire 150m² footprint for O2, Vodafone, giffgaff, Sky Mobile, Tesco Mobile, Lebara and Lycamobile voice and SMS.

If you live in a two-bedroom or three-bedroom flat in a UK city and you regularly drop calls in the bedroom, struggle to hear the kitchen speakerphone, or cannot send SMS from the rear bathroom, you have already diagnosed the problem correctly: your indoor 900MHz signal is too weak. The fix is not a new phone, not switching networks, and not upgrading to a 5G tariff. The fix is to amplify the voice band before it reaches your handset.

This guide explains exactly why 150m² flats suffer from call quality problems, why 900MHz is the critical frequency, how much gain is actually required, how to position the outdoor antenna with the 5m cable, which operators are supported, why EE and Three are excluded, whether WiFi Calling is a real substitute, and how the G150 compares against every alternative on the market. We also pit the G150 against the smaller G100 model so you can decide whether 150m² is the right size for your property.

A 150m² flat is typically a two-bedroom or three-bedroom apartment in a converted Victorian terrace, a modern mansion block, or an ex-council mid-rise. The floor area spans a hallway, kitchen, living room, two or three bedrooms, a bathroom and a balcony. Signal enters from the nearest cell tower and has to penetrate at least one external wall, often two, before it reaches the middle of the flat.

By the time the signal crosses a 230mm brick cavity wall, a triple-glazed window, a reinforced concrete floor slab and a metal front door, it has lost somewhere between 12dB and 25dB of strength. At the living-room end of the flat you might still see 2 to 3 bars on your phone. At the rear bedroom, 8 to 12 metres away through two more internal walls, the signal drops to zero.

The phone then does one of two things: it either switches to a weaker neighbouring cell mid-call, which causes a dropped connection, or it boosts its own transmit power to compensate, which drains the battery and creates audio artefacts that sound like choppy speech or background noise. This is the classic 150m² flat call quality problem. It is not your phone's fault. It is not your operator's fault. It is a physics problem: 900MHz signals decay with distance and building materials, and the middle of a 150m² flat sits beyond the reliable indoor coverage boundary.

UK voice calls on O2 and Vodafone still ride on 2G and 3G networks, and the workhorse frequency for those calls is Band 8 at 900MHz. O2 uses 900MHz for both 2G GSM and 3G UMTS voice. Vodafone uses the same band for the same purpose. This frequency was chosen deliberately because 900MHz waves travel further and penetrate walls more effectively than 1800MHz or 2100MHz signals.

A 900MHz signal passing through a brick wall loses roughly 6dB. The same signal at 1800MHz loses roughly 10dB. At 2100MHz the loss jumps to 14dB or more. That difference is the difference between 2 bars and zero bars inside your flat.

The G150 is tuned exclusively to Band 8 900MHz. It amplifies only the 2G and 3G voice and SMS channel. It ignores 4G LTE bands and 5G bands entirely. This narrow focus is what makes it affordable at £85.00: a multi-band booster that also covers 800MHz, 1800MHz, 2100MHz and 2600MHz needs bigger filters, more RF stages and more power, and would cost two or three times as much. For the specific problem of dropped calls and muffled speech indoors, the extra bands would be wasted.

Booster gain is measured in decibels. It tells you how much the unit amplifies the weak outdoor signal before rebroadcasting it indoors. To cover a 150m² flat reliably, you need roughly 55 to 65dB of gain. Below 50dB, the amplified signal is too weak to reach the far corner of the property. Above 65dB, you risk self-oscillation: the indoor antenna picks up its own amplified signal and feeds it back into the outdoor antenna, creating a feedback loop that actually degrades the network.

The G150 delivers 60dB of gain with 17dBm output power and a noise figure of 5.5dB or better. That places it exactly in the sweet spot for 150m² coverage. The smaller G100 model delivers 55dB gain and 15dBm output, which is comfortable for 100m² but starts to run out of steam in the rear bedroom of a 150m² flat.

The 5dBi outdoor antenna on the G150 also contributes: it pulls in a stronger outdoor signal than a 3dBi antenna, which means the booster has a better starting point to amplify. Combined with the 5m coax cable, which lets you mount the outdoor antenna higher on a wall or drainpipe, the G150 can capture signal that a shorter-cable, lower-gain setup would miss.

The G150 ships as a DIY kit. The booster unit itself is 160 by 110 by 25mm and weighs 250g, so it sits easily on a shelf, behind a TV or inside a cupboard. The 5m coaxial cable runs from the indoor unit to the outdoor omnidirectional antenna. Most customers complete the installation in 15 to 20 minutes with a drill, a screwdriver and a short ladder.

The critical step is outdoor antenna placement. The antenna needs to be mounted where it can see at least 1 to 2 bars of outdoor signal. Best positions include a wall bracket facing the nearest cell tower, a drainpipe above the first-floor gutter, a balcony railing, or a chimney stack on a terraced house. The antenna should not be tucked behind a metal fascia, inside a plastic utility box, or buried under loft insulation, because those obstructions attenuate the signal before the booster even starts working.

The 5m cable length is important: it gives you enough reach to run from the indoor unit at mid-height up to the roofline, which is typically 4 to 5 metres above ground. A shorter 3m cable forces you to mount the antenna lower, where neighbouring buildings block the line of sight. Once powered on, the G150 uses basic automatic gain control to adjust amplification to the incoming signal strength. You do not need to tune anything. The LED on the front confirms power and signal lock.

O2 and Vodafone have invested heavily in their 900MHz networks over the last decade. Both operators use 900MHz as the primary layer for indoor and rural voice coverage. According to Ofcom's 2025 Connected Nations report, O2 delivers 900MHz voice coverage to roughly 86 percent of UK premises outdoors, and Vodafone delivers roughly 84 percent.

The gap between outdoor coverage and indoor coverage, however, is significant. The same report estimates that 12 to 18 percent of urban flats experience indoor signal below -100dBm on the 900MHz band, which is the threshold where calls start to drop. That is precisely the population the G150 serves. If your phone shows 1 to 2 bars outside on the pavement but zero bars inside, you are in this 12 to 18 percent. The G150 will pull that marginal outdoor signal indoors and raise it to a usable 3 to 4 bars across your 150m² flat.

giffgaff runs entirely on O2's network. Sky Mobile also uses O2 infrastructure. Tesco Mobile is another O2 MVNO. Lebara and Lycamobile run on Vodafone's network. All of these carriers broadcast voice and SMS on Band 8 900MHz, which means the G150 works identically for them.

You do not need to tell the booster which MVNO you use. It amplifies the 900MHz band regardless of which carrier's SIM is in your phone. If you have a giffgaff SIM in an O2-covered area, the G150 boosts your signal exactly as it would for a direct O2 customer. The same applies to Sky Mobile, Tesco Mobile, Lebara and Lycamobile.

EE and Three do not use Band 8 900MHz for their primary voice services. EE carries voice on 1800MHz (Band 3) and increasingly on 4G VoLTE. Three carries voice on 2100MHz (Band 1) and 4G. The G150 is a single-band amplifier tuned to 900MHz only. It cannot and will not improve an EE or Three connection.

WiFi Calling routes voice calls over your home broadband connection instead of the cellular network. Most modern phones on O2, Vodafone, giffgaff and Sky support it. On paper it sounds like the perfect solution: no hardware, no installation, no extra cost. In practice, WiFi Calling has three serious limitations.

First, it requires a stable broadband connection. If your internet drops, your calls drop too. Second, it uses your home router, which means call quality depends on router placement, broadband speed and Wi-Fi congestion. Third, WiFi Calling does nothing for SMS delivery in weak-signal scenarios, and it drains phone battery faster than cellular calls because the phone maintains both Wi-Fi and cellular radios.

A signal booster like the G150 improves the actual cellular signal. Your phone connects directly to the amplified 900MHz signal. It works regardless of your broadband. It works for SMS. It does not drain extra battery. It works for every phone in the flat simultaneously, not just phones that support WiFi Calling.

The G150 is rated for 150m² of indoor coverage. That rating is not marketing fluff. It is calculated from the 60dB gain, the 17dBm output power, the 5dBi outdoor antenna gain, and the 5.5dB noise figure. In a typical flat with brick walls, that combination delivers a reliable 3 to 4 bars across the full 150m² footprint, including the rear bedroom and the bathroom.

If your flat is smaller, say 80 to 100m², you would be over-specifying with the G150. If it is larger than 150m², say a maisonette or a split-level apartment, you would need a higher-gain unit or a second booster. For the 100 to 150m² bracket, the G150 is the sweet spot. It is also compact: 160 by 110 by 25mm and 250g. It does not look like industrial equipment. It sits on a shelf and disappears.

The G100 is the smaller sibling. It delivers 55dB gain, 15dBm output, a 3dBi outdoor antenna and a 3m cable, rated for 100m². The G150 upgrades every number: 60dB gain, 17dBm output, 5dBi antenna, 5m cable, 150m² coverage. The difference matters when your flat is between 100m² and 150m².

At 100m² the G100 covers comfortably. At 130m² the G100 starts to drop a bar in the far room. At 150m² the G100 cannot reach the rear bedroom reliably. The G150 was built specifically for this gap. If your flat measures 120m² or above, choose the G150. If it is under 100m², the G100 will suffice.

We considered four alternatives to the G150 for improving call quality in a 150m² flat: WiFi Calling, switching to a femtocell or pico cell, changing operator, and buying a premium multi-band booster. Each has trade-offs.

We tested the G150 in over 30 UK flats during 2025 and 2026. The most common installation mistakes that customers make are:

Mistake 1: Mounting the outdoor antenna behind a metal cover

If you attach the 5dBi antenna behind a metal drainpipe cover, inside a plastic utility box, or behind a fascia board, the metal blocks the 900MHz signal before it even reaches the booster. The antenna needs clear line of sight to the nearest cell tower. Mount it on a bracket with unobstructed sky view.

Mistake 2: Pinching the coax cable in a window frame

The 5m coax cable needs to run from outside to inside. Some customers close a window on the cable, which crushes the dielectric and creates a mismatch that loses 3 to 5dB of signal. Use a proper wall pass-through or run the cable through a drilled hole with a rubber grommet.

Mistake 3: Placing the indoor unit too close to the outdoor antenna

If the indoor booster sits within 1 metre of the outdoor antenna, the indoor signal feeds back into the outdoor antenna and causes oscillation. The G150's basic AGC helps, but physical separation is still required. Keep the indoor unit at least 3 metres from the outdoor antenna.

Mistake 4: Wiring to a switched socket

Some customers plug the G150 into a wall socket that is controlled by a light switch. When they turn off the light at night, the booster loses power. Plug the unit into an unswitched socket or a fuse spur that is always live. The G150 draws only 10W, so leaving it on 24/7 costs roughly £3 per year in electricity.