I was just having a conversation with cow orkers today about this, except for game consoles instead of phones. The fact is that commanding leads in market share (see the PS2 in 2005) can evaporate quickly when a hot new competitor comes along (see the XBox 360 in 06, and then the Wii now.)

Despite these shifts in market share dominance, they're all legitimate players, because tools and libraries exist to make ports easier, and because there are enough customers out there that you can be profitable even if you target a single platform.

Likewise, I can see room for 3-4 major players in the smartphone market. Blackberry has their own niche and loyal base in the enterprise, so they'll probably stick with that. Android doesn't have any gee-whiz hardware out there yet, but don't underestimate Google. Symbian will probably remain a minor player and maybe be squeezed out by the re-emergence of Palm.

I think Apple should take this seriously.