Inbound calls from PSTN

[tlg]

I am just setting up Voxalot for use with a simple ATA (Netcomm V300).
I have the ATA successfully registered to Voxalot using my six digit Voxalot account number.
Outgoing calls via dial plans to various VSPs are working fine.

What I am trying to set up now is incoming calls from PSTN to my Voxalot number.

I have Default Call Forward rule set to:
sip:123456@voxalot.com (where 123456 is my Voxalot acct number)
and no other Call Forward rules.

I dial the local Sipbroker access number (Bris Aust 61 7 3018 2881) from a PSTN phone and get the voice prompt, then I enter *010 123456

However the ATA phone doesn't ring and I get a very choppy ringing tone in the PSTN phone.

Is there something in the set up that I have missed?

Thanks for any help.