I'm guessing that you are routing the 8 prefix calls to SP1. Did you add (Mvg1) to the phone digit map? If you did, the 8 prefix is stripped during the digit map processing then the outbound route will route the call to SP1. You need to add the same rules to the digit map, but without stripping the 8 prefix. The outbound route will strip the 8 and route the call to VG1.