Incoming stopping after 1 ring?

[mori]

Hi all.
I've setup my netcomm V85 to connect to au.voxalot.com successfully.
I have Oztell setup as a provider as sip2.syd.net2max.com. It is active, and registered.
Outbound I have no problems whatsoever, and if I register the phone directly with Oztell, I don't have any inbound problems.

However when the handset is registered with voxalot, and I have an inbound call into Oztell, down through VoxALot, to the handset, the phone rings once, and then hangs up and it registers as a missed call.
On the outbound handset, its a silent line.

V85 settings:
protocol: G729
reg expire: 900
rtp packet interval: 40ms
sip domain name && proxy addr: au.voxalot.com

oztell settings:
voxalot registered in the web dialer for outbound.

firewall settings:
UDP and TCP port 5060 forwarded to my phone.

Also, the connection between my V85 phone and voxalot seems to disconnect every 5 minutes? whats the go?

Thanks,
Brian