[VoiceOps] Anyone from TMO monitoring?

Is anyone from T-Mobile monitoring? We're running into an issue where a call that's handed-off to TMO gets back a "480 Temporarily not available", of course failing the call. I've compared a call where this isn't happening with a call where it is, and the only thing I see different (other than access IP's) is that on the "bad" call, the audio's set to INACTIVE, but on the "good" call, the audio is SENDRECV. Any thoughts or input would be greatly appreciated! Thanks, Mark