But I digress. We're not going to use that phone much, so I decided to use the $25 recharge card on my own phone. T-mobile's system is odd: Apparently, the cost per minute is calculated based on last recharged amount. So when I recharged with the $25 card, my cost per minute rose from 10 cents per minute to 14 cents per minute. And a quick check revealed approx. 250 minutes = $30. Then I added $100 to my phone, making it drop back down to 10 cents per minute. So now I've got $130 = 1300 minutes.
Lesson of the story here? If you use T-mobile to-go, and you happen to have random recharge cards on hand, do those first, then recharge with $100 to get the best cost per minute deal.