With the imminent arrival of the Apple iPad, Apple will have 3 iPhone OS devices however developers are limited to just 100 UDID slots for ad-hoc distribution says the Icon Factory’s Craig Hockenberry on his blog , reports an article over on tipb.

Basically there is some concern over how many UDDI slots developers get to use, for instance if your company owns a developer account with Apple there will be 3 apps, the iPhone, the iPod Touch and the iPad but you only get 100 slots in total not 100 slots for each app.

The article then goes on to explain just how quickly the allotted 100 UDID slot can be used up and the fact that Apple only frees up UDID slots only one time per year which adds to the problem. Also any lost devices, beta tester or developers that have left the company or dropped out further equate to wasted UDID slot which won’t become available for up to a year.

Thus with the launch of the Apple iPad, many devs who have already hit the maximum slot allotment and their slots don’t free up before the 3rd of April, means they cannot register any new UDIDs and thus can’t register iPads to test.