Hi m8 .i beleive the s/ware you are looking for is called m.o.b.i.l.e but as for where to get it im not sure .this s/ware only works on a BT line.your other alternative is to use call divert to your mobile phone .
some people say it cuts them off others say it dont the other downside to using call divert is you have to pay for the diverted part of the call...
hope this helps