while(<DATA>) {
    s/[^\d]+//g;     # remove non-digit characters
                     # only digit characters remain

    m/(.{0,10})$/;   # find as many as 10 characters,
                     # starting at the right

    print $1,$/;     # print the found digits
}

__DATA__
800-1212
1-800-800-1212
1(800)800-1212
1 (800) 800-1212
1 800 800 1212