I would purchase a 2600 XM with enough Ram and flash to support the voice software you probably need a NM-1V or nm-2v depending if you want to test fax machines or analog calls between the router with a fxs card and if you get a fxo card you can create your dial-peers to dial outside. There are also some old cheap mc3810 routers that do t1,e1 and fxs modules on ebay so you can possibly get two and do more testing...