SIP call transfer in Asterisk

Hi Guys,

I am trying to find alternate solutions for Asterisk Blind/Attened transfer (Based on REFER),currently the way it works is fine but biling is biggest problem.

Basically i would like Asterisk to behave only like PSTN GW so in that case i am thinking of Handling all transfers/REFERS and all call handling stuff at some B2BUA that will control Asterisk GW. Hopefully i can bill customers at Asterisk GW side.

Anyone can please suggest me what is best fit for B2BUA Asterisk/ Opensips/ Free Swicth/Yate . Which can gives me full control of proper SIP handling and scalable soltuion.

Please feel free to comment with your crazy ideas.

Idea is like this SIP user A ----> opensips proxy-----> B2bUa ------> Asterisk GW—> exernal world.

To put in simple terms on carrier side (ISP) side all VOIP customers should be able to transfer calls based on REFER.

I look forward to hear from you all.