Most reports indicate that Apple and Google Android phones are gaining ground at the expense of other smartphone companies. RIMM (Blackberry) does not have the level of consumer interest or app store capability that are driving the current market. Palm, the early leader, was recently acquired by HP but it appears their primary interest is in the Palm WebOS operating system for tablets and not Palm phone hardware. In fact at the time the acquisition was announced, HP dropped their plan for a Windows tablet in favor of the "Streak" based on WebOs.
The choice is between a tightly controlled product from Apple where hardware, operating system and applications are well integrated and the wide open approach of Google where numerous companies make the phones which can operate over several carriers. There are currently five different versions of Android; each of which can be modified by the manufacturer. It's not easy to answer the question "exactly what is an Android phone?"
Having AT&T as the only carrier has definitely hurt Apple but it is likely that will change and Verizon or T-Mobile will be an option before the end of the year.