I disagree with the conclusion of the article. Right now, I try free apps often, and upgrade to the paid versions a reasonable fraction of those tries. If Apple allowed billing from within iPhone applications, it would make me uncomfortable about downloading new apps to try them out. I haven't even considered the AT&T GPS thing precisely because of the stealth billing/continuous billing involved. A la carte purchasing of an application's features might bring more revenue to a few developers, but it would decrease the revenue of the entire ecosystem.