Comment 6 for bug 278485

One more or less straight foward way would be to never use a default route prio lower than the current lowest route ... this would enforce that previously used default route would still be the default route when more devices become active.

Another fine tuning would allow the user to enforce default route by clicking on the network ... e.g. if NM auto-connects to lets say wirelss while you are connected to GSM it will keep GSM default route the default; but if oyu explicitly connect/click on the wireless it would take over the default route.