* How about building and running your own kernel on your phone. Is that something you would be interested in? Most Android phones can do that.*
No, I'm interested in browsing the web, reading and sometimes replying to my email, checking my calendar, doing online banking, finding restaurants via Yelp, reading my Instapaper queue, checking my RSS feeds, reading and replying on Twitter, listening to and downloading new podcasts I subscribe to, occasionally reading ebooks, listening to my own music and Internet radio, getting turn by turn navigation and sometimes walking or transit directions, and checking in on Foursquare.
In other words, I want a smartphone. Ideally, I want one that works without dorking around with a damn kernel recompile. Android phones can absolutely do all of those things (without damn kernel recompiles). And, darned if iPhones can't just as easily.
In practice, applications aren't lock-in. Data is lock-in. What Apple can do to piss me off is locking in my data, which is a potentially grave concern with iCloud. But just about everything I mentioned above is stuff that would take me about a day to migrate from iOS to Android or vice-versa, because nearly all of it involves open data formats.
Being able to put a new kernel on your phone? Sure, it could be fun. But when push comes to shove, the best thing a smartphone can do for me is to make its inner workings as invisible as possible. When I want to spend time cursing at a Unix shell prompt, that's why I have Arch Linux. Not on my phone.