[Asterisk-Users] Call forwarding

[Kenneth van Grinsven]

Hi,

I've just installed asterisk a few days ago and figured most of it out, but I can't seem to forward calls.
In the setup before I used asterisk, when people called my (ISDN) number and I didn't answer the phone in 4 rings, the call would be transferred to my cellphone. I ofcourse made that setting by once dialing, from the ISDN line, *610*XXXXXXXXX#, XXXX being my cellphone number.
The advantages of those transfers is that 
1) on my cellphone I see the original called ID
2) after the transfer the ISDN line is not busy anymore.

I tried to achieve the same in *, but so far no luck.
I know I can transfer calls like this (my setup now), in extensions.conf:

exten => s,1,Dial(SIP/21,14)
exten => s,2,Dial(Modem/g1:06XXXXXXXX,30)

Which first tries to dial SIP extension 21 for 14 seconds (my regular phone), and then dials my cellphone. It works but has 2 disadvantages; on the cellphone I can only see the phone number of the * server calling out, not of the person who is actually trying to reach me, and when transferring calls this way both my ISDN lines on the BRI are used for this connection (1 incoming and 1 outgoing).

Now I am not too familiar with modern telco equipment, but is there a way * can "tell" the telco's switch to transfer this call to another number, just like it would in the *610* setup?

Regards,

Kenneth van Grinsven