General :: Selective Internet Calling (app Or Widget)?

I have an SGS2 running ICS and have setup my android's SIP client (internet calling) in phone > settings > internet call settings ("Accounts" and "Use internet calling", at the bottom).

I call many international numbers through sip. If I set the option "Use internet calling" to "Ask for every call", then every time I dial a number it asks whether to use "Mobile phone call" or "Internet call". If I choose the latter, then the call is made through my sip provider saving me lots of money.

It would be really useful if there was an app that would intercept calls to certain numbers I configure and change to internet call mode on the fly. The "prefixer" app does something close with prefixing/suffixing numbers.

Alternatively, I would also be happy with a widget that allows me to switch that phone option between "Ask for every call" and "Only for Internet calls" when tapped, so I don't have to navigate through menus all the time. For a dev this shouldn't be that hard I presume since it would just alter an existing OS option.