Thanks - meant to say "iPads." I corrected it above. I need to stay with ATT to keep my grandfathered unlimited data for my phones. But if I can get my iPad connection for less at T-Mobile, I'd move them over.
Truth be told, by not willing to change plans, there isn't much AT&T can do for your iPads - those old plans don't have certain features and are conceptually very different (the new data-bucket-style plans let you add iPads relatively inexpensively, especially if you don't plan to use much data). There are also a lot of people that will not give up their unlimited data, but are only using a few GB/month, so the current plans may actually be a better value overall, especially if you have multiple devices. Unlike some carriers, AT&T rarely does much in terms of special promotional plans, except some retention plans. Besides that, they'll grandfather you on your current plan indefinitely, which can be good or bad (for me, it would've actually been more to move from Mobile Share Value to Mobile Share Advantage, but for a friend of mine it was a bit cheaper to move). You can always go to a corporate AT&T store and have them run the numbers—despite some popular opinions, employees there do not have any sort of incentive to force you to move.
That being said, if you just want to keep a little cellular data on the iPad for cheap, T-Mobile is a good alternative. Since iPads are unlocked, they can work with carriers that are compatible with your hardware. In the case of the iPad 2 and 3, they're GSM, meaning you have the option of AT&T and T-Mobile. Newer models have additional radios and frequencies so they are a bit more universal (my iPad Pro works on all four carriers).
Here's what you'll need to do (you could try it with your iPad 3 and always swap the SIM card into your iPad 2 to try that, too):
- Go to a Best Buy, Walgreens, Walmart, etc. and buy a T-Mobile prepaid SIM card. They typically run $5-$10 and are the same ones that will work for prepaid phones and tablets. I've bought a few from Best Buy for work and a personal one from Walgreens and they come in a little kit, usually near the prepaid phones and refill cards.
- Remove your AT&T SIM card from the iPad and pop in the T-Mobile one. They tend to be the kind that punch to different sizes, so make sure you don't make it too small (your iPads use micro SIMs, like the iPhone 4, while newer iPads use nano SIMs, like the iPhone 5 and later).
- Once the SIM card is in, it may take a second, but the carrier should change to say T-Mobile in the upper-left corner. Once it does, you can go to Settings > Cellular Data and you should be able to tap "Manage T-Mobile Account..." (If it doesn't, you might need to turn on cellular data).
- For best results, you can turn off Wi-Fi to force the SIM card to connect to a cell tower. From there, T-Mobile will walk you through creating a prepaid account (email address and password) and then you can choose to add data or go for the "later" option. That will give you 200MB/month for the life of the device. They're not picky about it, but it auto-renews each month and doesn't require any payment information on file. Since it's a little bit of data, I suspect the idea is for people to try out their network and also keep SIM cards active to potentially add more data later. People have even moved SIM cards to newer iPads and kept this plan, so the "for the life of the device" is a very loose definition.
- If you find coverage/features/etc. isn't what you want, you can always pop the AT&T SIM back in the iPad and continue using it with AT&T (so if you are going to cancel those lines from your AT&T account, wait until you verify that you are happy with T-Mobile).
At worst, you'll be out $5-$10 for the T-Mobile SIM card, but otherwise it could be an inexpensive way to keep a bit of cellular data available for those devices. Additionally, if you need more data, you can add a non-recurring "data pass" via a credit card, debit card, or prepaid card (those almost work like iTunes Gift Cards) and that will be in addition to your 200MB (so if you buy 3GB/$30, it will last a month, giving you a total of 3272MB). After that, it will go back to 200MB/month for free.
The nice thing is that most iPads (except for the Verizon/Sprint-specific iPad 2/3/4) can work on multiple carriers without any special work as long as the carrier has a prepaid or postpaid tablet plan. This is great for world traveling (since most of the world is GSM-based) and giving some options with newer iPads. Apple put both CDMA and GSM radios in the iPad Air and newer, allowing them to connect to just about everything (LTE is GSM-based, so that's why Verizon and Sprint have started issuing SIM cards, the CDMA radio will kick in for connection to older towers). Some people have used this as a way to get the best coverage possible when traveling—they'll have a couple of active prepaid SIM cards and use the one most appropriate for that area or carry a phone from one carrier, iPad with another and use hotspot mode on each if necessary.
Obviously, your iPads are a little before that benefit, so your choices are probably just AT&T and T-Mobile (maybe some regional carriers?), with the iPad 3 getting LTE on some frequencies.
