String Escaping in Pattern Matching

Hey gang,
 I have three possible inputs:

   18005551212
   +18005551212
   8005551212

Right now I am using this to strip off the +, 1, or +1:

INSERT INTO ... VALUES(SUBSTRING(usernumber FROM '^\\+?1?(.*)'));

This works perfect but I get all of these in the log:

WARNING:  nonstandard use of \\ in a string literal at character 181

If I change to this as per the doc example right above the 9.7.3 header
on this page:
  http://www.postgresql.org/docs/8.2/static/functions-matching.html

SUBSTRING(usernumber FROM '^#+?1?(.*)' FOR '#')

I get NULL inserted but no WARNING's.

A point if the right direction would be appreciated.

Thanks,
Matthew