Help with Fritzbox settings (for irishvoip.com)

Moved from Pure Telecom to Vodafone a few months back (solely on the basis of price and sorry I did!). Vodafone made a balls of porting my number over from Pure, so I signed up to irishvoip to have at least some working telephone service.

Previous posts here indicate that others here did similar after moving from Pure. However, I can't figure out what settings to use to get the voip service to work (irishvoip's support has declined to assist and just gave me a link to their kb listing generic settings). So far, it looks like the number isn't registering. Settings I used are:

OTHER PROVIDER>

TELEPHONY PROVIDER| irishvoip.com

TELEPHONE NUMBER FOR REGISTRATION| 3531*******

INTERNAL TELEPHONE NUMBER FOR THE FRITZBOX| 01*******

and

USERNAME| 3531*******

AUTHENTICATION NAME| (left this blank)

PASSWORD| (as given by irishvoip.com)

REGISTRAR| irishvoip.com

PROXY SERVER| (left this blank)

Any idea what's missing and where? Any help gratefully received.