OK got a chance to swap my SIM and try this

Some comments - in North America the carriers charge for incoming calls and texts so currently the call/SMS monitoring is insufficient for PAYG in North America.

In swapping SIMs from PAYG to contract, being able to hide the icon completely while the contract SIM is in place is preferable. Yes, I can disable the updating but I still have the icon showing my UK PAYG balance showing even though all the monitoring is disabled.
Additionally the only way to disable the icon action itself is to delete the 'balance' code. If this isn't done and the icon is accidentally pressed you get an 'unknown application' error. Although I never had the standby screen notification enabled, activating the icon while on the contract SIM seems to screw up my Billboard/Meecast on the standby screen.
I use Billboard and Meecast alot more than USSDbalance, and as it can't be properly disabled I'll be uninstalling until I need it...