Does anyone one know whether it is possible for me to reroute incoming calls on my mobile to another number?

Question

So that when I am at home (no signal) I can reroute my calls to my voip.

Answer 1

If you're on Orange they have a divert service called Everyphone which costs 8.5p to set up, but the diverted calls are free.

It's usually available to divert to other Orange phone or landlines, but VoIP may work.

If you're not with Orange you can set up a standard divert, but you will pay for the call.

Answer 2

It will most probably be possible (call forwarding), although you will be charged for the forwarded calls from your cell to the number in the (other) network to which it will be forwarded. Check with your mobile network provider, I am sure they will be able to help you out.

Usually, you can set call forwarding rules for a number of situations - when you are unreachable (no signal, phone turned off), busy, or when you simply just do not answer.