J,
There are several units which do what you want<some allow you to only call a
pre-programmed #, some allow you to call any # after entering a security
code, soem do a call back to a specific # before giving you a dial tone,
some have a built in amp. to boost the voice on both sides of the unit,
etc>.
Just a guess….wanting to use the 2 lines to avoid a toll call<A-B is free,
B-C is free, A-C is toll>?
Jeff