This function restrict numbers:

function ChkEmail( emailaddr ) {
	var objRegExp  = /(^[a-z]([a-z_\.]*)@([a-z_\.]*)([.][a-z]{3})$)|(^[a-z]([a-z_\.]*)@  ([a-z_\.]*)(\.[a-z]{3})(\.[a-z]{2})*$)/i;
	//check the address and return true if formatted ok
	return objRegExp.test( emailaddr );
}

This function allows a little more flexibility:

function ChkEmail( emailaddr ) {
	var objRegExp  = /(^[a-z]([a-z_0-9\.]*)@([a-z_\.]*)([.][a-z]{3})$)|(^[a-z]([a-z_\.]*)@  ([a-z_\.]*)(\.[a-z]{3})(\.[a-z]{2})*$)/i;
	//check the address and return true if formatted ok
	return objRegExp.test( emailaddr );
}

This one is wide open and only checks the basic syntax:
function ChkEmail( emailaddr ) {	
	var objRegExp = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
	//check the address and return true if formatted ok
	return objRegExp.test( emailaddr );
}

This funtion allows close to maximum flexibility:

function ChkEmail( emailaddr ) {
	var objRegExp = /[^\s@]+@[^\s@]+\.[^\s@]+/;
	return objRegExp.test( emailaddr );
}

function ChkPhoneUSDash( phonenumber ) {
	var objRegExp = /^[0-9]{3}[\- ]?[0-9]{3}[\- ]?[0-9]{4}$/;
	//check for desired phone format 999-123-4568
	return objRegExp.test( phonenumber );
}


if (! ChkPhoneUSDash( this.value )) {
	alert('Please check the phone number. The format should be 123-123-1234. Thank you.');
	setTimeout("f.Frm_Fld.focus();",1); 		// give time for user tab key to happen so we can move focus back
}
Note:
Alternate e-mail regex formulas:
/(^[a-z0-9]([a-z0-9_\.]*)@([a-z_\.]*)([.][a-z]{3})$)|(^[a-z]([a-z_\.]*)@([a-z0-9_\.]*)(\.[a-z0-9]{3})(\.[a-z]{2})*$)/i

- This version allows numbers after the letters in IE. It's big bug so far is that it allows name123@.com where the domain is left out.
\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b

- This one is more flexible and allows more flexibility in the domain suffix (e.g. com vs info).
\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*