Strikes me that it can’t hurt to have another number. And swapping cheap prepaid sim cards isn’t crazy if you pair the strategy with a free Grand Central number where you can change the number it forwards to at will.
Maybe it’s just the tech geek in me, and there’s no useful purpose to this, but $3.99 and $10 credit sure isn’t much lost.
Update: Flyertalk’s ScottC offers more details
It’s on the GoPhone plan, so there are 2 options:
No daily charge, minutes are $0.25
$1 daily charge, but minutes drop to $0.10 (daily charge only applies when you actually make a call) + FREE AT&T mobile to Mobile