Transfering calls to outside lines

I am in the process of moving my existing phone system over to Trixbox CE. I have a PRI thru the local carrier that will be cut over to our old number in the near future. The bulk of our calls come in on this number and will be going to a Queue that I have setup to support 10 incoming calls max. The trunk is setup to allow 10 lines for outbound calls. I will only be rolling out the new phones to a small group of people to answer the bulk of the calls and keep the old PBX intact with a few lines that hunt off one of its remaining numbers and then roll out other groups in phases. My intention is that if someone calls in on the new system they will transfer them out to the ring the old PBX for those folks to field their calls. My question is, when they transfer them out will that call still be "active" as a call in the queue tying up that line or is it now on one of the outbound lines of the trunk thus freeing up the queue to take more calls? Does this make sense or is there an easier way to accomplish this? Thanks!