Yes, I am using the external profile but it is a copy of the internal one and modified by me. I imagine that having the desired configuration it is irrelevant to use one or the other.
Yes, I would think the same.
Maybe you want to check with a sip trace if the registrations are ok and coherents with what the system expects...
Maybe there is a mismatch of some kind... (force registration domain name?)
Other than this, you probably need a consultant to look into it.
-giovanni