Well, there's now another way to add money to your amp'd prepaid account. BabbleBug.com just came out with an Amp'd topup that you don't have to enter any PINs to add to your phone...it's all done over the network. You still have to buy refills in increments of $20, $30 or $50 like normal Amp'd cards and I think Amp'd may have this feature on their own, but I'm 99% sure that if you refill via Amp'd you pay sales tax, and on babbleBug, unless you're in California, you don't, which is nice.

The refill is here:

Prepaid Cell Phones,Prepaid Cell Phone Plans & Prepaid Wireless Cell Phone Airtime Refill Minutes Online at Babblebug.com.

Though for some odd reason Amp'd leads the wrong way...but I'm sure that'll get fixed soon...