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Other than jailbreaking, I think there are a couple of methods.

1) If you fill up your pages with apps, but still have storage space for more, they should load on the iPhone but only be available using Spotlight to search for them. So fill up on 'visible' apps, then install the ones you want to hide.

2) This was inadvertent. My mom even stumped an Apple Genius the other day, when they were looking for the Notes app.

I had upgraded and gave my original iPhone to my mom ("Happy Mother's Day... here's something I don't want anymore"). Anyway, I deleted apps she wouldn't be interested in, and the result was several blank pages. The 'Notes' app, which the 'Genius' was looking for, was on the last page.

So, they saw a few apps on the home page, scrolled to the right and saw a blank page, and gave up, assuming the Notes icon was AWOL.

So, load up enough apps to have several pages, move the desired apps to the back, then delete the apps in between to create blank pages. I would have thought the blank pages would disappear (I think they do in the Simulator) but they didn't.
 
Jailbreak the phone and use SBSettings

To further clarify, you don't have to keep your phone jailbroken after you've hidden the apps you don't want. My phone is back to "stock," minus the Contacts, Weather, and Stocks apps. That setup even carried over when I upgraded to the 3GS.
 
I need a way to hide icons but have them still show up in Spotlight. That way I can show only my primary apps on the homescreen and use Spotlight as an application launcher for not-used-very-often apps. Any ideas?
 
I need a way to hide icons but have them still show up in Spotlight. That way I can show only my primary apps on the homescreen and use Spotlight as an application launcher for not-used-very-often apps. Any ideas?

if your jailbroken (i assume you are) download an app from cydia called spotbrite. Adds a recently opened section to the top of spotlight, and allows it to find hidden apps
 
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