No incoming calls on RTP300

[energyx]

I am trying to use an unlocked RTP300 until I receive a replacement for my RT31P2. I have it registering with the Central SIP server, but it is only registering one port. I can make calls, but incoming calls won't ring in. Any idea what setting under the Voice tab in the config I am missing?

Thanks
Chris

*edit* I just realized I only need one port for each line on the device. Once I disabled the second line, it worked fine.