fabero,
I have done this in AnyCut using intents, should be able to do the same by sending intents from B4A. Note you need to use escape codes for the URI formatted phone number.
SERVICEMENU
Action: android.intent.action.DIAL
Data: tel:*%23*%230011%23*%23
Dials (but does not actually initiate the call) the number given (or the stored voicemail on the phone).
bluejay