[Kamailio-Users] how to prepend area code into a local call phone number

[Jinsong Hu]

Hi, Sir:
  In the US, assume a person from 1-408-1234567 is dialing phone number 
1234568.
how do I figure out the caller's country code and area code and prepend to 
the local number ?

  I tried
prefix($(from.user{s.substr, 0, 4}));

  and openser reported as  parser error in config file, bad argument, string 
expected.

Jimmy