I'm not sure if that's absolutely true. 50% of the customers who switched networks to get the AT&T iPhone 3G left Verizon to do so.I think the real competition here is between AT&T and Verizon, not a couple of phones that will be inconsequential in a year. In that regard, there is no comparison. Verizon's network is lightening fast and AT&T's is 10 pounds of crap in a 5 pound sack.
http://www.efluxmedia.com/news_iPhone_3G_Prompts_Users_to_Switch_to_ATT_25944.html
FWIW, if you add the BlackBerry + iPhone marketshares, you only account for 20% of people out there.The majority of people out there either have an iphone or a BB.
57% - Symbian phones
17% - Blackberry (RIM)
12% - Windows Mobile
07% - Linux
03% - iPhone
02% - Palm
01% - Misc
http://www.gartner.com/it/page.jsp?id=754112