Ting (855.846.4389) is offering a free $5 Starbucks card to any AT&T Wireless customer just for checking if their phone could work on Ting.
The card is actually an eVoucher that will be emailed to you rather than a physical card. To get it, go to this page and enter your phone's IMEI (serial number) along with your phone number (to verify that you are an AT&T customer) and the email address you'd like you Starbucks voucher sent to. When you enter you information, Ting will tell you if your phone will work on the T-Mobile side of Ting. There's no opligation to actually switch to Ting and there's a box to un-check if you don't want to recieve marketing emails from Ting.
I'm not sure what Ting is actually checking, probably which of T-Mobile's bands your phone supports. Every AT&T phone supports the 1900 Mhz band that T-Mobile uses for voice, SMS and data (3G in most markets but only 2G in some). Recent AT&T phones also support some or all of T-Mobile's LTE bands 2, 4 and 12. However the most important thing about using an AT&T phone on T-Mobile is that the phone be unlocked. As far as I know, there's no way to determine a phone's locked or unlocked status from the IMEI.
AT&T GoPhone prepaid customers should be eligible for this offer and I think AT&T MVNO ones likely are too by virtue of being on the AT&T network.
You can find your IMEI by entering *#06# in your phone's dialer as well as on a sticker under the battery or back cover and on the box the phone came in. It's also available in the menus of most smartphones in the following locations:
- Android: Settings > About device > Status
- iOS: Settings > General > About
- Windows Phone: Settings > About > More info
Related post: Prepaid Operator Profile: Ting