Grandfathered Alltel Accounts

No Alltel/CDMA phone will not work on at&t

But, you can use pretty much any GSM phone (at&t phone or a carrier unlocked phone). It will be a hassle... But it can be done

You can use the at&t next program or you can buy a phone out-right from a manufacture or at&t (if buying out-right don't buy a software bloated phone with slow, limited or no updates from at&t).

1. No "new" GSM or at&t (GSM) phones will work correctly with any account provisioned as a grandfathered Alltel/ATN rate plan. (See #3 below for reason)

2. if you replace a the phone in question with any at&t branded phone "that was given free to former alltel customers that kept their alltel/atn contracts" then you can just swap the sim. (See #3 below for reason)

3. The phones given to former alltel customers when they transitioned were crippled by at&t both in the phone itself and by the provisioning ...

No 4G LTE ever (although at&t promised the FCC and alltel customers that former Alltel customers would have LTE access).

Former Alltel / ATN customers maximum data is limited to 2G and 3G speed (although the phones are set up to lie and display 4G even though they are only receiving 3G HSPA and 3G HSPA+ ).

4. No at&t store is permitted (they should get a warning pop-up) to modify the account nor do they have the ability to modify the provisioning of the account or any line on the account (any changes will corrupt the account because the rate plans don't really exist... they were custom built to match the Alltel rate plans) unless they are replacing it with an at&t individual/family/share plan.

5. In order for former Alltel customers to get a new device working with AT&T with an Alltel grandfathered rate plan:

Alltel customers can activate pretty much any new GSM phone on at&t but only voice will work... no data services will work (no Media Messaging and no Internet).

Whats needs to be done is the provisioning team must add the "NextGenphone APN" to "each line activating a new/replacement device. 

This will get the device data services working (but still the device will be crippled/ speed limited but you'll notice the new device will show the correct 3G acronym for the connection rate instead of 4G) 

I now have unlocked Developer (Pure) Edition Moto X 2's and an unlocked International/World Edition Motorola NEXUS 6's working on the AT&T network with our grandfathered Alltel rate plan (unlimited data). Although the lines/phones are crippled/ speed limited to 3G or less I still use 30-80 GB a month.

https://forums.att.com/t5/Phone-Device-Upgrades/refused-activation-of-new-att-compatible/td-p/4198474