I will build a voip network by use SER+asterisk in China. but I don't connect my sip network to pstn , this is don't be permission in China. if you have a asterisk and have pstn access, then you can contact me about copartner. I will let my user that he want to dial to pstn will use your pstn . and I need your rate to pstn and I only hope can get a little part. I hope negotiate about it. Thank you.