Javascript Submit executes form.submit despite errors

Good Day All,

I am having an issue were when I click submit the f.submit() at the end of my code is executing, despite the fact that it should have errored out and returned false?

function f_Submit()

{

var f = document.forms[0];

if ( f.User_Name.value=="" )  

 	{ 

		alert ("Please enter your Name.");

		f.User_Name.focus();

        		f.User_Name.select(); 

		return false;

}

if ( f.Contact_Number.value=="Please update your info in the Global Address Book (names.nsf)")  

 	{ 

		alert ("Please enter your Phone Nunber.");

		f.Contact_Number.focus();

     			f.Contact_Number.select(); 

		return false;

}

if ( f.Contact_Number.value=="" )  

 	{ 

		alert ("Please enter your Phone Nunber.");

		f.Contact_Number.focus();

     			f.Contact_Number.select(); 

		return false;

}

f.submit();

return true;

}

I cannot find where my error is in this script.

Any help would be appreciated as awlays… Just need that second set of eyes… Or wish mine worked…