US Mobile | The next generation wireless network

Now that I know that Verizon blocks backup calling (among other things) for its own customers too, I figured someone must have other workarounds. I was expecting to find a Magisk module but maybe this is even better.

Disclaimer: I haven't tried it myself but it claims to enable backup calling without root.

I see that the preferred network type selection is missing now in the Verizon network preferences. I haven't used it as much lately but sometimes I use it to disable 5G when it's acting up.

It's still accessible in the service menu.

It can also be added back by editing the carrier config (here we go again). Set hide_preferred_network_type_bool to false.

This one doesn't sound like an oversight.

This doesn't work anymore on Android 14. For whatever reason, it sounds like Google really wants you to buy an iPhone is you need backup calling. This issue "probably" is only for "Warp 5G" (Verizon) but I haven't tried "GSM" (T-Mobile) yet.

~~This post is about using a secondary data-only (e)SIM to make voice over WiFi (VoWiFi) calls on Android.

I have a Pixel 7 phone. It supports dual active SIMs (either SIM+eSIM or eSIM+eSIM). I assumed if I had VoWiFi enabled on USMobile and an eSIM with international data, I'd be able to make calls internationally. I discovered it was not that simple.

To test before my trip, I simulated being out of coverage by telling my primary SIM to use only 3g data, which is no longer available in my area. I enabled the data only eSIM and disabled WiFi. To my surprise, I was not able to make calls or text.

I found some posts that mentioned "backup calling" but I did not see that option in my network settings. I went to look at the carrier config settings in /data/user_de/0/com.android.phone/files and noticed that carrier_cross_sim_ims_available_bool was set to false. Since my phone is rooted, I was able to edit the file and set it to true.

I rebooted. I still couldn't make calls or text.

I then went back into network settings and noticed that a new option appeared. Just below "WiFi Calling" there was now a new option called "Backup Calling". I enabled that, waited a bit and noticed that the signal icons had changed. I was able to make calls and texts. It worked just like WiFi calling!

A few additional observations:

1. You will only see the backup calling option if you have 2 SIM cards enabled. It will disappear if you disable the second SIM. Interestingly, the value is retained so you don't have to keep setting it if you have reason to disable and reenable the data SIM.

2. The edit to the carrier config seems to get reset sometimes. It happened to me twice so far. It may be the monthly firmware updates or it might just be something the carrier pushes out occasionally. This is over the course of several months so it's only a minor inconvenience.

3. I don't know how to fix this for unrooted phones. (Edit: but you might try this.

4. This is for Android users. IPhones seem to support it out of the box.

5. Based on a recent trip with a Samsung S22, it appears that Samsung phones will also use a data eSIM as data for VoWiFi even though they have no backup calling option. I should caution that it wasn't very reliable for us but each phone is different. My Pixel, by contrast, worked well throughout the trip.~~

I've put together a little python script to monitor pool data usage and top up automatically.

https://github.com/dbrand666/usmobile-lifeguard

It can be run standalone but I've set it up to run under docker compose for stability. I've been running it for a few months and it's working well for me. The authentication token does expire occasionally and when that happens the script will abort. You need to grab another one and restart the script.

It has a dryrun flag which runs everything but won't actually top up. Leave that set to true until you're happy with what the log is showing. Even once you set dryrun to false, it will give you 10 seconds warning before topping up so you have a chance to kill it if it's doing something unexpected.

It's only set up to do one pool, mostly because I only have one pool, but if anyone has more and is willing to test I'd be willing to add support for multiple pools.

Comments, bug reports, suggestions, etc are welcome.

Here's a trivial Tasker project I'm using to keep tabs on the data and days remaining for a pool. It displays as a "persistent" notification that updates every 15 minutes. It's here if anyone else is interested.