Hi My All Friend on Greats PBXinfo

I need your Idea,
my friend's office have a Panasonic PABX TDN1232 series, and have the Computer LAN. The computer LAN has Been Interconnecting with The Other Computer LAN on another Building which have a PABX system too ( Panasonic TA308 ). How I can help my Friend's PABX system to interconnection ? How to make the Panasonic TDN 1232 connect with TA308 via VOIP of Computer network ?
Ok thanks to All of you who has to read my Subject, and I'm very Glad if you want to reply it