Regex for Phone numbers

Regex for Phone numbers

1. xxx-xxx-xxxx         grep -o '[0-9]\{3\}\-[0-9]\{3\}\-[0-9]\{4\}'  file.txt
2. (xxx)xxx-xxxx        grep -o '([0-9]\{3\})[0-9]\{3\}\-[0-9]\{4\}'  file.txt
3. xxx xxx xxxx         grep -o '[0-9]\{3\}\s[0-9]\{3\}\s[0-9]\{4\}'  file.txt
4. xxxxxxxxxx           grep -o '[0-9]\{10\}' file.txt
grep -o '\([0-9]\{3\}\-[0-9]\{3\}\-[0-9]\{4\}\)\|\(([0-9]\{3\})[0-9]\{3\}\-[0-9]\{4\}\)\|\([0-9]\{10\}\)\|\([0-9]\{3\}\s[0-9]\{3\}\s[0-9]\{4\}\)' file.txt

- Found online, and put on my git for reference.

Credit goes to Raullen Chai
on 
http://stackoverflow.com/questions/2269586/grep-with-regex-for-phone-number