How To: Use a GSM carrier (AT&T/T-mobile) in conjunction with CDMA (Verizon) on i-Phone with e-Sim activation.

Feb 19, 2009
The Woods of NY
Quick back story to get the full picture...
I have a Verizon Wireless Post Paid account for many years with a "Verizon" network unlocked i-Phone 13 Pro Max.. Verizon sells i-Phones with all the network bands, but they are software network locked to Verizon but only for 60 days. On the 61st day the i-Phone will be automatically network unlocked.

Where I live in the mountains the closest Verizon tower is over 8 miles away, AT&T has a tower about 5 miles way. I also have a Verizon Network 4G LTE extender for my home and that extender gives Verizon LTE access to any CDMA verizon phone even if it is a MVNO (Mobile Virtual Network Operator) aka a carrier that uses the verizon towers under a different name within a few hundred feet of the extender.

All is well when the internet and power is working, but trees falling down with intense storms taking out power and internet is a real possibility. Once that happens my i-Phone turns into a paper weight so updates from the electric company, work on call, or whether ect I can not receive because... well verizon no service.

After some trial and error and trying a couple different GSM MVNO companies with e-Sims this is how I was able to use my main Verizon account to piggy back off the att/tmobile towers when Verizon service is non existent for data and calls.

First make sure your I-Phone is network unlocked aka no sim restrictions, and your Verizon account has Wi-Fi calling enabled.

Then sign up for a GSM carrier of your choice that offers e-Sim compatibility. (I-Phone XS or newer) I tested gsm Red Pocket last week - That would be my recommendation for a GSM AT&T service provider just because of the online activation process that actually worked, and it includes 1GB of data for $10 a month. I had a Physical AT&T tracfone sim working in the past but recently Tracfone was bought out by verizon and they are now only offering CDMA verizon sims and no e-Sim yet so I had to look for another gsm provider. You would need to give the GSM carrier the "AVAILABLE SIM2" number under: General: About, and that number would be under your main sim number near the bottom. I choose Boost because it "appears" they use both the T-mobile or AT&T towers "depending". Also 2GB of data is under $12 a mouth. but again, if you only are looking for a GSM provider for backup and 1GB of data would be enough per month, Red Pocket is the way to go as the automated website activation e-Sim and data all worked the first time. Boost not so much. a few calls later boost works fine now, but was not a simple to activate a GSMA red pocket.

Here is my Boost Mobile Plan:
Screenshot 2023-07-04 at 6.50.34 AM.jpg

I will say right off the bat.... Almost ALL of these MVNO provides have NO idea on how wireless technology works. The service reps will read from a script... and it always starts off with... "Check for updates" and "Power off and back on" your device.. Also boost mobile activation website never worked for me and had to call "support" a couple times, one for the activation and another time to get data working.. "If" you can tolerate the multiple calls and have a little time or knowledge to troubleshoot your own problems, it will work, but it's not easy. It was and is worth the aggravation for me because simply put, once the internet or power goes down.. Verizon has zero usable cell service this area unless I travel miles away..

I then turned off the 5G band for the GSM boost provider and only use LTE for battery life and data saving. I kept the Verizon 5G UWB enabled because that is my main service with premium priority high speed data, and enabled "Data Switching" Also make sure Verizon WI-Fi calling is enabled in your settings on I-Phone to use Wi-Fi calling as I am doing.


And here are results:


the 2.2 Mbps is not going to break any speed records, BUT it is fast enough to enable the Verizon Wifi and make decent quality calls also all a apps and websites work fine. Hotspot also is acceptable -ish with the 1 maybe 2 bars of service it receives on LTE.

For me and in this area with limited as in no options, "slow" a steady is a winner, and is much better than nothing..

If you have any questions I will try to help answer them for you.

Does Verizon still have CDMA radios in the RAN(Radio Access Network)? They started a hard push to get rid of all CDMA in 2019 and forcibly started removing CDMA devices in 2020. All carriers want to reallocate the spectrum used for the old 2G and 3G radios to 5G NR (New Radio).
I do not believe so. I might of used the wrong term "CDMA", as that term I grew up on and it did mean Verizon at the time, and GSM was ATT/T-mobile.

But Verizon no longer uses the 3G (CDMA) Technology, (Dec 2022 discontinued) even though in this area the 3G signal went further. and they will not activate or give you support on 4G Non-VoLTE Devices. Verizon only will activate and give you support on 4G LTE or 5G/5G Ultra Wideband devices.
Same for ATT, they have already mostly shut down the 3G in my area. I think right now it is all about which "band" of radio your phone supports instead of GSM vs CDMA.