Okay, here is my question:.

I have 30 SIP connections connected to asterisk from the outside,
with real telephone numbers.

I also have 30 SIP clients (Softphones, IP Phones, Adapters),
What i have done, is to set up 

[stig]
exten => 21985863,1,Answer
exten => 21985863,2,PlayBack(transfer)
exten => 21985863,3,Dial(SIP/2001|90)
exten => 21985863,4,HangUp
exten => _X.,1,Dial(Sip/${EXTEN}@stig|90)

Like that in extensions.conf

And the phone configured like this in sip.conf:

[2001]                                                                                                                                        
type=friend                                                                                                                                   
username=2001                                                                                                                                 
secret=Password Here                                                                                                                                
host=dynamic                                                                                                                                  
context=stig                                                                                                                                  
mailbox=102     

Okay,
now i have 30 different clients, and lines
each of those 30 clients have their own numbers to the
outside.

My problem is, i want to have internal numbers
like 2001, 2002, 2003, ETC.

How can i configure one place those internal numbers,
so i dont have to configure it for each of the clients?

Thanks for the help!