I was having bad call problems with my set up using Netgear Router and Linksys adaptor/router and was advised to buy a Draytek Vigor all in one modem/router for VOIP.
But I need SIP details from my provider ie Vonage and they won't give them to me. Are they allowed to do this? They say I can only use their equipment.

This causes me problems as I use the incoming no for business and it is being used in advertising etc.

Any ideas or similar experiences?

I had the same problem with Vonage a couple of years ago, they wouldn't give me the sip details either. In the end I moved to another provider.

If your having call problems then maybe you don't have the right ports forwarded to your adapter. Try putting the Linksys adaptors IP address in your Netgear routers DMZ?