I have owned the T-Mobile G1 since October. I had been looking for a replacement for the T-Mobile Wing for some time, and being a fan of open source and Linux, I was very excited to read about Android (even exploring Android development using their SDK), and even more excited to learn T-Mobile had the initial offering of an Android based cell phone.
I pre-ordered the G1 as soon as I could. It wasn't just the fact the phone was open source, or that it ran Linux, although nearly limitless development potential and extreme stability were my number one and number two reasons. I was so tired of my Windows Mobile phone. The Wing was the best option for T-Mobile at the time I purchased it, so I put up with it. I simply had no choice. In fact I had purchased the phone on craigslist.org, from a Google employee, and I had asked him excitedly "when is the Google phone coming out?" The announcement came several months later.
My Wing just wasn't a very good phone. It was slow (crippled for battery life), it crashed often or froze. There were many quirks, but it was a decent phone. I couldn't sink easily with my Linux desktop, so I didn't. The web browsing was crippled and very slow, and most of the web didn't work right. There were rarely updates. After all, money is made when a user upgrades, not updates.
It did have many features, some my G1 does not have, although many of these features were poorly implemented, or didn't work correctly. Is a feature that does not work correctly really a feature?
After using the G1 for several months, it is the best T-Mobile offering for my purposes, and if only for the fact it's open, and due to iTunes, better than the iPhone.
The integration with Gmail and Google calendar are a God send for me. I don't need to worry about syncing anymore, less my files, which I can do by plugging the phone and copying and pasting. This did not work easily, if at all, with my Wing and Linux.
For me, the phone is great, and the free applications make it even better. The only challenge I have with this phone is it's short battery life, even when using it on the EDGE network with no GPS or WiFi. The phone does charge with a mini-usb cord with any computer, so this makes things easier. In fact, I typed nearly this entire post with the G1 before I stopped due to low batter life. The phone had been used moderately for the previous four or five hours and lasted the rest of the day.
But I would rather have a shorter battery life than a crippled or slow phone, and, in my opinion, the G1 is the best phone T-Mobile offers.