I know the VigorBX 2000n is now pretty long in the tooth so this is a bit of a shot in the dark.

It has served us well until recently when an incoming call can be seen on the extensions (Grandstream GX2130s) and can be answered but the phone doesn't actually ring audibly.  It's on the latest available firmware 3.9.1    Has anyone come across this before?

Alternatively, the router works just fine so is it possible to disable all the IPPBX functionality so we can use a third party PBX (such as a Grandstream UCM6200)?

Thanks
Keith