Prologue

Despite being an uncultured American I limited the search in my original post to GSM phones so my research could be used worldwide; this had the knock-on effect of narrowing potential carriers. Sprint is in hell and Verizon still uses its own special tech, which leaves T-Mobile and AT&T.

To be clear, I only researched 4G/5G compatibility with these carriers - which shouldn't be much of an issue as both T-Mobile and AT&T killed 3G support last year; while AT&T killed 2G support years ago T-Mobile says it will kill its 2G support at some undetermined time in the future - best not to rely on it.

Battle of the Bands

According to PhoneArena, AT&T 4G operates in the 700, 850, 1700, 1900 and 2100 MHz frequencies - its backbone is 700 MHz band 12/17 [1], but relies on 1900 MHz band 2 and 1700/2100 MHz band 4/66 in urban areas [2]. PhoneArena also has a record of all of AT&T's 5G bands, but for the purposes of this post I only care about the 850 MHz n5 band.

T-Mobile 4G operates in the same frequencies as AT&T, with urban areas using its backbone of 1700/2100 MHz band 4/66 but suburban areas using 700 MHz band 12 and rural areas using 1900 MHz band 2, but T-Mobile additionally has access to 600 MHz band 71 which it uses for a slight amount of 4G service. T-Mobile also has other 5G bands not covered here, but I want to reference its use of 2.5 GHz n41 and its development of 600 MHz band n71.

Thus, when looking for a GSM phone that works on 4G/5G in the US, you need compatibiity with these bands and frequencies:

For the best cross-network performance support for 4G bands 2, 4/66 and 12/17 is vital, with 12/17 more important for AT&T and 4/66 more important for T-Mobile.

Phone Compatibility

At this point I compared the frequency support of the phones I discovered in my last post to each carrier's supported bands to get this result:

Thus the Teracube 2e and Fairphone 4 are preferable if the best performance on AT&T is required, but if 5G support is necessary there's only one game in town.

Finding A Carrier

I developed a small checklist when searching for carriers conducive to clandestine use:

• Must have yearly plans available (decreased maintenance burden)
• Must have low-usage plans available (this isn't a primary communication method)
• Must be cheap (ditto)
• Stretch goal: can buy activation kit/top-ups in-person (no paper trail)

Direct offerings from AT&T/T-Mobile were awful, but I found a number of MVNOs that fit the bill:

I additionally found free service offers from FreedomPop and TextNow, but FreedomPop requires renewing its service every month and TextNow's service is ad-supported.

Like the last post in this series I don't really have a conclusion - you can pick up Red Pocket, FreedomPop and Mint Mobile SIMs in store at least, but you have to buy plan renewals online. I guess I'd suggest going with FreedomPop if you have very slight needs and can handle renewing your service every month, otherwise Red Pocket may be the best option.