i got good experience with Onesuite.com prepaid cards
Rates are very competitive.
Can be use on any phones as long as touch tone phones.
Can be use across US, Canada, Puerto Rico, Guam and Hawaii. International access is also available to most parts of Europe, South America, Australia and some parts of Asia.
Low rates 24/7
You can refill your account thru calling their support hotline or by logging in to your online account.
Onesuite also has a voip feature that you can use with out additional charge. And only $2.95 monthly if you want to use it voip incoming calls feature.