JENNA JAMESON ACCUSER 'She Beat Me With A Brass-Knuckle iPhone!'

Jenna Jameson allegedly wanted to beat down her assistant  -- and yep, there's an app for that.

Jameson allegedly went all Naomi Campbell on the transgender gofer, but with a dangerous twist ... a BRASS KNUCKLES CASE on her iPhone 5 ... according to legal docs.

Shocking details of the arrest have now emerged in Britney Markham's restraining order request, filed by attorney Adam Krolikowski. She claims Jameson barged into a Newport Beach salon and started bitching at her, and eventually punched her in the stomach and back with the weaponized device.

Markham claims Jameson then threatened, "I'll f***ing kill you." 

The assistant says she definitely was the worse for wear, landing in the hospital.

Here's the thing: Brass knuckles are illegal in California, so Jameson could be in felony territory ... but she has an interesting defense -- the brass-ass add-ons are an accessory, not a weapon. 

Fashion -- it can be really dangerous sometimes.