If you're building a custom theme, I'd recommend creating custom page templates - one each for an About and a Contact page.
This gives your end users some flexibility. They can define their own page and select your template - so "About" could be used for "About," "About Me," "Our Story," etc. No need to know which page will be used for the about page in advance.
Just define two extra php files in your theme:
about-template.phpcontact-template.php
Then make sure the files include a header that looks something like this:
<?php
/*
Template Name: About Page
*/
?>
... The rest of your regular template file continues below ...