I've been using
Gizmo Project (which is the same company as sipphone.com) as my VOIP provider along with SJPhone as my pocketpc softphone and they have $0.01/min calls to the US. The quality is fine for me. Also, if you sign up for area775.com you can get a 775 area code call-in number for free.
You have to drop in $10 at a time, but it's been worth it for me. I use it when I'm running low on cellphone minutes. $0.01 is a lot cheaper than $0.45 when I go over on Verizon.
I just turn my Axim upside down so the speaker is at my ear and the mic is at my mouth, and it feels like a big, flat cell-phone!
/sam