i can phone from 1000 to 3300 (but i don’t have sound, i don’t hear hello world)
I can phone from 1001 to 3300 (but i don’t have sound, i don’t hear hello world)
I can’t phone from 1000 to 1001
I can’t phone from 1001 to 1000
You will need to provide more details (a sip trace, possibly using sip set debug on) to work out which packet wasn’t getting through, however you might want to note that some soft phones have broken imlementations of sip re-invites.