Elan Telecom have experienced difficulties getting SIP services to work correctly via BT Home Hub and Sky Sagem routers.
Sagem Routers are usually supplied by Sky Broadband. Most of the older models have a setting called SIP ALG enabled by default and there is no easy way to disable this.
BT Home Hubs have remote access disabled unless it is via a chargeable BT Support Service.
Any customers wishing to use Elan Telecom's hosted PBX system via either of the above should consider upgrading to a suitable Router as Elan Telecom will not support SIP Services over unsuitable networks.