I am using orbtalk and sipdiscount on a grandstream 2000 through a netgear mimo router and plusnet adsl.

I can use sipdiscount fine for incoming and outgoing calls, but for some reason I cannot receive calls on orbtalk, only make them?

I fired off an email to orbtalk about it but have not received a reply as yet so does anybody have any idea what my issue could be?

Have you tried setting the SIP port to 5065 on the ATA for the OrbTalk account and forwarding ports on the router to the ATA?