This Regular Expression matches..
1-246-424-5699e125
1-246-424-5699x125
12464245699
1-246-424-5699E125
1-246-424-5699X125
424-5699e125
424-5699x125
424-5699E125
424-5699X125
and more.....
Thanks to http://regexlib.com/RETester.aspx?regexp_id=898