function checkForm(f) {
	
	var errors = new Array();

	if (f.elements["carrier"].value.length == 0) {
		errors.push("Please enter your carrier.");
	}
	
	if (f.elements["device"].value.length == 0) {
		errors.push("Please enter your device.");
	}
	
	if (f.elements["serialNo"].value.length == 0) {
		errors.push("Please enter your serial number.");
	}

	// display errors or submit form
	if (errors.length > 0) {
		var msg;
		
		if (errors.length == 1) {
			msg = "Please correct the following error:\n";
		} else {
			msg = "Please correct the following errors:\n";
		}
		
		for (var i = 0; i < errors.length; i++) {
			msg += " - " + errors[i] + "\n";	
		}
		
		alert(msg);
		
		return false;		
	} else {
		return true;	
	}	
}