[Serusers] How to change the calling number

[Mac]

Hello,

I am trying to change the calling number string on SER.
To be more precisely: i need to have a possibility to freely change the 
contents xxxxxxxx of the following line
From: "abababa" <sip:xxxxxxxx at 10.10.10.10:29577>.

Could you tell me if it is possible to obtain this goal or point me 
somewere i can get an answer.

Thanks a lot,
Mac.