I  recently had a project that needed to validate Irish mobile phone numbers. Here is the PHP function I used in case anyone needs to do the same again.

The function returns FALSE if the number is not in a valid format or else it returns the mobile number in the format 003538XXXXXXXX. It can deal with odd formated numbers such as (086) 1234123, +353861234123 etc.

function validate_number($number) {

	$number = preg_replace('/\D/', '', $number); //Strip all non numeric characters

	$length = strlen($number);

	// Strip the 00353, 353 or 0 from the start of the number
	if ($length == 10) // 08XXXXXXXX
	{
		$number = substr($number, 1);
	}
	elseif ($length == 12) // 3538XXXXXXXX
	{
		$number = substr($number, 3);
	}
	elseif ($length == 14) // 003538XXXXXXXX
	{
		$number = substr($number, 5);
	}
	else // Not a valid number
	{
		return FALSE;
	}

	if (preg_match('/8\d{8}$/', $number)) {
		//Number must have an '8' followed by eight other digits i.e. 8XXXXXXXX
		return $number;
	}
	else // Not a valid number
	{
		return FALSE;
	}
}