[asterisk-users] distinguishing users by their domain

[Ricardo Carvalho]

In extensions.conf I want to implement a dial plan that distinguishes 
the users that wish to dial a PSTN number by their own domain, so that 
john at domain_A goes out to PSTN by a different DID than john at domain_B.

I tried the following line, but that doesn't distinguish between 
domains, and then if john at domain_A or john at domain_B dials some PSTN 
number, both calls goes out using same DID (did1):

exten => _[0-9]./john,1,Dial(SIP/${EXTEN}@did1,120)

I tried then using the following lines:

exten => _[0-9]./john at domain_A,1,Dial(SIP/${EXTEN}@did1,120)
exten => _[0-9]./john at domain_B,1,Dial(SIP/${EXTEN}@did2,120)

But those syntax doesn't work.
How can I do it? Any clues?

Thanks,
Ricardo.