asterisk users - Jan 2005 - Extension.conf, sip.conf and contexts.

Hi,

Does the context defined in sip.conf have to be the same context to which
the extension belongs to in sip.conf?

I have all my local SIP phones in context=local, and are in a context call
local in extensions.conf. I then signed up with a few voip providers and I
only wanted to allow one of the SIP phones to use it, so I moved him into
his own context in both files. I also included [local] in entensions.conf.
He can call all the other phones, and is able to call out using the voip
providers, but the other SIP phones are unable to call him. 

Am I missing something very obvious?

Regards

David Norton