Just noticed some promotions from the "softphone" SIP providers.
Mouthmun prepaid services has a promotion till 31st Dec - rates starting at 0.75 baht
Call Cafe's prepaid softphone offers 0.50 baht to Thailand and 0.95 baht for international.
Cat2Call also running a promotion till 31st Dec starting at 0.91 baht
Looks like a price war is brewing ?
Have not tried and cannot vouch for their call quality though.
Cavaet emptor !