[aquark]

I'd go with Twilio too ... only issue is you need to have upgraded your account to port a number:

http://www.twilio.com/faq/porting

But since credit's don't expire, and you can always find another use for Twilio in the future it is a good bet.

[johns]

You can upgrade without paying until your balance runs low. Just set up auto-renew and you can buy a number.