Are you sure about what you are asking???? SS7 is the kind of signaling protocol used when you are handling few hundred channels at a minimun.
Anyway, the VOIP that you are using is the one doing SS7.
From there to PSTN, you will need one or two data links or circuits to the PSTN company to carry the signaling.
But again, there is no much point to do it unless you are above several T1 capacity.
The company where I work have over 50 T1 ‘s, all of them PRI and we consider that SS7 is a overkill for us.
Good luck!!!!