#!/usr/bin/perl

use strict;
use warnings;

use 5.010;

for (q(Name Vornamesip:0813893511@b2b.domain), q(0813893511sip:0813893511@b2b.domain)) {
    /(.*)?sip:(\d+)\@.+$/;
    say '' . ($1 eq $2 ? $1 : '') . $2;
}