Interestingly, Apple does not own the trademark to iPhone (if my recollection is correct).. it's Cisco.. and they even had a row over this because Cisco's subsidiary made products of the same name.
Anyways, to appraise, my views are the following:
1) Notwithstanding the controversy over .mobi domains, iPhoneRingtone.mobi is spot on... technically, you can't get any better than a "ringtone" domain for a particular mobile phone, with a TLD that spells out what it's for (.mobi). I'd give it a multi reg-free amount
2) iPhoneAccessories.net is something that would be definitely in vogue soon enough, since everyone and their dogs would want an iPhone and by extension, accessories as well. So particularly for a store/ecommerce site, this would certainly be perfect. The .net extension is what kills it, imho, BUT the name itself is worthwhile nevertheless. I'd give it mid to high $xx at the very least. If developed, far more.
3) iPhoneBid.net is like the above, only less so... could be worthwhile for an auction site and aftermarket for iPhones and accessories... not as valuable as the 2 above, but still worthwhile, imho.
Good luck with those!