Dialing Rules: Prepending Country Codes And Selecting Trunks

I've struggled and got what I wanted, but not quite... I could use some
suggestions please.

On pbxes.com, I have two three trunks: one VOIP provider in UK (A), one in US(B) and one in Japan(C).

I'd like to set up so that:
When someone dials 44xxxxxxxx, get the 44 stripped and a 0 prepended to make a UK domestic number 0xxxxx and when 7xxxxxxxx is dialet, get 007 prepended go on trunk A.

All calls made to 81 go to trunk C and get 00 prepended and all other calls go out on trunk B.

Any suggestions?