Regular expression to match standard 10 digit phone number

Question

I want to write a regular expression for a standard US type phone number that supports the following formats:

###-###-#### 
(###) ###-#### 
### ### #### 
###.###.####

where # means any number. So far I came up with the following expressions

^[1-9]\d{2}-\d{3}-\d{4} 
^\(\d{3}\)\s\d{3}-\d{4} 
^[1-9]\d{2}\s\d{3}\s\d{4} 
^[1-9]\d{2}\.\d{3}\.\d{4}

I am, however, not quite sure if the last one is correct for the dotted check. I also want to know if there is any way I could write a single expression instead of the 4 different ones that cater to the different formats I mentioned. If so, I am not sure how to do that. And also how do I modify the expression/expressions so that I can also include a condition to support the area code as an optional component. Something like

+1 ### ### ####

where +1 is the area code and it is optional.

Answer 1

 If you are also interested in matching on unformatted numbers just make the separator character class optional as [\s.-]?

^(\+\d{1,2}\s)?\(?\d{3}\)?[\s.-]?\d{3}[\s.-]?\d{4}$

Matches the following

123-456-7890 
(123) 456-7890 
123 456 7890 
123.456.7890 
+91 (123) 456-7890

If you do not want a match on non-US numbers, then use:-

^(\+0?1\s)?\(?\d{3}\)?[\s.-]\d{3}[\s.-]\d{4}$