asterisk users - Jan 2007 - asterisk 1.4: gui registration differs from non-gui

Hello, everyone.
I'd like to ask how does asterisk 1.4 with GUI register itself at the
provider's end (when I mark a checkbox 'register' while creating a
"Service Provider"). Before I used to write something like:
register => 924980111:xxxxxxx@sip.provider.com/924980111
in sip.conf. Having that line, asterisk would execute
exten => 924980111,1,.....
when receiving the incomming call to 924980111. However, when I create a
provider with the GUI and mark a checkbox 'register' that doesn't
happen. When I call 924980111 the extension 's' is executed.
Please, could anyone write if it is possible to achieve the same
behavior from gui.
Thanks.