Sonim XP3 (XP3800)

The Sonim XP3 (XP3800) has two versions; the Sprint and the ATT. The XP3's specs say:

The XP3 is on ATT's list of phones that will still work on its network after they phase out 3G in February 2022 ( I don't see ATT's list distinguishing between the two versions; the ATT version and the Sprint version.

Could I use the Sprint XP3 on carriers that use the ATT network, now and after ATT phases out 3G, like TruPhone or FreeU? You see 'new condition' Sprint XP3s are $30 on eBay while ATT XP3s are more than double of that.

Good question, dst11. I don't know the answer.

I've spent a few minutes perusing the AT&T list you linked to-- thanks for that! Lots of interesting incliusions, and lots of notable devices that aren't on the list. I'm really tired of having my phones declared obsolete by one or more carriers....

Doesn't Sprint phones have CDMA capabilities?

What will CDMA do? Isn't AT&T (and AT&T MVNO's) GSM?

I run the IMEI of several Sprint XP3 phones I saw on eBay through FreeUp's IMEI checker and all were rejected.

I have a Sonim XP3 Sprint-version that I got unlocked on Amazon.
I started using it with an AT&T simcard last year.

Three times in the past few weeks, AT&T has disabled my outgoing-call
functionality, redirecting all calls to customer support, where each
time I would go through the process of refusing the free VoLTE-comatible
phone they're offering (a crappy smartphone, I assume), and demanding
that they reactivate my account, as it's not February 2022 yet.

Apparently the Sprint version of the XP3 isn't on their "compatible phones" whitelist.

Rumor has it that many phones that AT&T will not let you use with an AT&T account will work just fine with a MVNO using the AT&T network.
I haven't tested this yet.

This is a major pain! I've been watching AT&T's whitelist of phones, hoping to see some evidence that they're loosening up on restrictions-- but so far, they're not.
It's true that most AT&T MVNOs are not being as strict for now, although working VoLTE will be a requirement. I don't know how long that will last.

...and I probably won't any time soon. I just activated a US Mobile (over TMobile's network) SIM in the phone, and I'm gonna see how it works for me. Got my first-ever VoLTE icon on the phone.

So, you could use the Sprint version of the XP3 on ATT (or an ATT MVNO). I thought you couldn't. Good to know!

Something I don't understand: why is ATT offering you a free VoLTE phone when the phone you use, the XP3, supports VoLTE. Am I missing something?

Someone on reddit had a similar problem: Sprint/T-mobile sent them a letter saying their XP3 will stop making voice calls after they shut down CDMA and phones without VoLTE will no longer work. But customer service admitted the XP3 will continue to work after the CDMA shutdown. Could ATT be pushing people towards crappy VoLTE phones hoping they don't like them and buy new phones?

I have used the Sprint XP3 on AT&T in the (very recent) past, but, according to AT&T, it won't be "supported" on AT&T when they disable 3G.

I strongly suspect that the Sprint XP3 has the full capability of doing AT&T-VoLTE, but AT&T's network uses a whitelist to determine what phones will work, and the Sprint XP3 is not on the whitelist. The AT&T version of the XP3 is. There may be a hack to get around this (e.g. maybe it's possible to install AT&T-XP3 firmware on the Sprint-branded XP3), but I'm not really aware of one.

My phone didn't report VoLTE support until I moved it off of AT&T.

I don't have any technical insight on the different versions of the XP3, but I wanted to say that I think there is a larger issue of how certain carriers might be leveraging the decommissioning of 3G and the need to have VoLTE capable phones to achieve the same goals they used to achieve with restrictive phone lock policies. Now that they have to comply with strict legal requirements on when phones must be unlocked they instead get phone manufacturers to punk the specs and software to ensure that even if they comply technically and legally with unlocking requirements, the end-user still won't be able to easily move a phone from one carrier to another.

You can see this with other carriers like Visible/Verizon. They market certain cheap phones that are unlocked but only work for voice on Verizon's VoLTE. Verizon is even worse on this front than AT&T because the software is set up to lock out APN editing, so some of the phones can't be used on Verizon MVNOs.

Fortunately for me, iPhones are purposely made to be cross-compatible with all carriers and Apple doesn't work with carriers to tailor its IOS to specific carriers.

Even if one can install new firmware, the IMEI would still not clear the whitelist check. (AT&T still will see it as a Sprint XP3.) If AT&T sweeps the system for whitelist checks on MVNOs, as they're currently doing on AT&T's self-owned providers, it would likely still get suspended.

I'm a little confused. What does "self-owned" mean here?

AT&T owns AT&T Prepaid of course, but they also own Cricket: properly, Cricket is not an MVNO. The AT&T corporate device restrictions (whitelist) have applied to Cricket just as they do to AT&T Postpaid. At this point, AT&T hasn't forced MVNOs to apply the very restrictive whitelist system. (We're just starting to see evidence that they might, with one Tracfone user reportedly receiving a warning about an AT&T network phone not on the whitelist.)

Ah... in short, "self-owned" means "ATT-owned". got it.