My brother is travelling to part of Southeast Asia (Thailand, Vietnam, Cambodia, and Laos) and I've put together a spreadsheet that compares telephone costs to and from the US.

The spreadsheet is far from being comprehensive, but I thought that the PrePaidGSM.net community might be interested in it.

The providers include those that provide toll-free number + PIN, and those that use callback.

Long distance telephone services compared:
CallbackWorld
Ekit
Enlinea
Expat Telecom
GlobalPhone
Globaltel
Kall8
OneSuite
Telesys

Spreadsheet can be found at:
http://numsum.com/spreadsheet/show/26045