Using wondrous items to qualify for feats and prestige classes

[Jadeite]

Since you can use statboosters to qualify for feats, would you also be able to use magic items to qualify in other ways?
Could you use a Dark Blue Rhomboid Ioun Stone to qualify for Sleepless Detective?
Could you use a Hand of the Mage to qualify for Arcane Strike?
Could you use a Greater Hat of Disguise to qualify for Mystic Theurge?

[Kazaan]

No, because stat-booster items, after 24 hours, graduate their bonuses to "permanent" which means it actually increases the relevant ability score and qualify you for feat prerequisites, increment "x times per day" abilities based on that stat, etc. There's no such vetting process for special abilities granted by items; they just do their thing from the moment you don them and never become "permanent".

[Majuba]

The Dark Blue Rhomboid would work, since it actually grants you Alertness. The others would not work as they do not actually let you cast a spell.

Same as always, if you lose the prereq, you lose the class abilities and can't progress.

[Xagroth]

For the Prestige Class, I'm not sure, but the feats are clear: You can use Magic Gear to qualify for feats, but you can't use the feat if you somehow lose the gear that gives you the requirements.
For the prestige class... that could be even worse, losing whole levels because you lost your +2 Dex ioun stone, frankly. So I would rule that as a "no" for the player's sake (not to mention my own, since I would feel compelled to not try to take that piece of gear from the PC).

Also, please do note that you need to wear the item for 24 hours before the bonus being considered "permanent".

[James Risner]

Jadeite wrote:

Could you use a Dark Blue Rhomboid Ioun Stone to qualify for Sleepless Detective?

Could you use a Hand of the Mage to qualify for Arcane Strike?
Could you use a Greater Hat of Disguise to qualify for Mystic Theurge?

Yes

No

No

If you lost the DBR, you lose everything from Sleepless Detective.