There's a new free refill card with prepaid phone purchase offer at T-Mobile.com
This time it's a free $30 refill with your choice of two $99.99 refurbished Android phones. The offer is supposed to be valid from today through Thursday 5/31/12.
The eligible phones are the Samsung Dart and the T-Mobile Huawei Comet. These two phones are about as basic as an Android phone can be; low-resolution QVGA (240x320 px) screens, 3 MP fixed focus camera, 600 Mhz processor and dated Android 2.2 OS but at an effective cost of $69.99 they are also as inexpensive an entry into the world of Smartphones as you will find today. And you can use them on any T-Mobile prepaid or postpaid plan.
I don't have any experience with either phone but on paper the Dart seems like the winner. It's new, thinner, and has a slightly larger screen than the Comet. You can compare the specs on Phonescoop.
Promotion has ended.