Busy signal on incoming FXO

[Dataworks]

Perplexed on this one: customer has 2 FXO lines ("a" and "b"), both are forwarded to auto-attendant (Quadro M8L). When a call comes in on "a", a second call to that number will be busy for the length of the previous call. If calling "b", auto-attendant picks up regardless of the status of "a". I thought that once the call is picked up by auto-attendant line "a" should release the FXO and be, fo lack of a better term, a SIP call. Am I wrong or do I have something configured incorrectly?

[ghomf]

you need to speak to your service providor and make sure you have hunting on both lines .