Reg.Asterisk and exisitng traditional PBX use


I have traditional PBX unit. and have asterisk PBX with T1 card. In Tradional PBX, i have around 16 lines and with some number extensions. Right now i have astetrisk installed with two sip phone lines (broadvoice). if i plan to go with entire asterisk PBX for my organistion, then by what ways, i can make use of the traditional PBX with asterisk pbx (integeration). Also i do not want set this tradional unit idle. someway , i want to make use of that.

Please guide me, by what ways i can make use this traditional PBX with asterisk. ?

Thanks in advance.