I use both an iPhone and G1 and I've also got an iPod Touch. I love the apps that are available for Apple's mobile platform and since I can use it on the Touch, I'm free to choose whatever mobile device to use to satisfy my other mobile and telephony needs.
A few years ago, switching between platforms can be a pain since each phone or smartphones have their own personal or calendar implementations that made it difficult to migrate information around. Today, it couldn't be easier. How is that possible?
Webapps. Especially with social sites like Facebook offering mobile version of their site and robust mobile versions of Google's apps, I can pretty much pick up any device with a decent Web browser and log in to whatever site I need.
What's more, this is only a small piece of cloud computing. Yeah, you might have heard a bit about that. Over time with Google pushing Chrome OS and Microsoft doing its own thing, it'll only be a matter of time before mobile computing on browsers become ubiquitous and a normal process of our lives.
Still, app stores aren't going to go away like Google predicts. There are still tons of issues to be worked out with Web computing that standalone apps just do better.
Note: Seriously, where the heck is Windows Mobile 6.5? With HTC possibly going 1/2 of its lineup with Android and other device makers going with Google's mobile OS, Microsoft seriously may be facing a lot of uphill battle here. Frankly, I'm getting a bit anxious here. Perhaps Redmond will come out with a WM-Zune-Xbox Mobile combo in 2010.