Don't recreate the wheel.  Search http://www.regexlib.com/Default.aspx.  
You're bound to find what you're looking for.

HTH
----
http://www.davefancher.com

hello
i think this code will help. U have to change the code a little bit
according to ur situation. in my case if the phone no. is valid then it will
return true. u can send return the validated phone no or error message.
Note: in this function i have use a string variavble ErrorMessage which is
member of the class. You have to handle it urself.

for any more help you can contact me via emal ---> cuirfan@hotmail.com

public bool Validity( string PhoneNo)
{
    bool flag = false;
    if( PhoneNo[0] >= '0' && PhoneNo[0] <= '9' || (PhoneNo[0] == '+') )
    {
        for(int i = 1; i < PhoneNo.Length; i++)
        {
            if( (PhoneNo[i] >= '0' && PhoneNo[i] <= '9') || (PhoneNo[i] == '_') ||
(PhoneNo[i] == '-') || (PhoneNo[i] == ' ') )
                flag = true;
            else
            {
                this.ErrorMessage = "The character \"" + email[i] + "\" is not allowed
in the PhoneNo";
                flag = false;
                break;
            }
        }
    }
    else
    {
        this.ErrorMessage = "First character must be between 0-9 or it may be + ";
        flag = false;
    }
    return flag;
}