Need a basic setup for home use.

Upgraded my router from the standard Sky one and can no longer use the router for voip unless it's the primary router in which I loose all functions/settings on my Asus router. What would be a basic budget setup with preferably being able to use the old number from sky and what would be the process for doing that? I get the occasional important phone call from a few places through my house phone and ideally need to keep it.