3COM ISDN Pro TA’s for voice only

I am configuring a 3COM ISDN Pro TA for both b-channels being used for voice. Are provider is Verizon (Nat.ISDN1).

Here’s where I am at:
Incoming call’s are coming in successfully. When going outbound, i seem to get a fast busy generated by theTA on one of the b-channels and sometimes nothing on the other.

Any suggestions???