Update 2009-12-10: Read Activate G1 without Android data plan, redux for fresh information.
The problem: You got your new T-Mobile G1, you already have a $19.99/month Total Internet data plan for yourself and a Family Time Unlimited Messages plan for the family. You don't need or want the new $24.99/month T-Mobile G1 Unlimited Web data plan, but it seems like you can't activate your new G1 without the special G1 data plan.
The solution: With one settings change, you can activate your G1 with the Total Internet data plan. Here's how.
Remove the battery cover and insert your SIM. Snap everything back together and power the phone on. Wait for the boot screens to disappear, and "touch the android to begin." Wait a moment, and the carrier connection signal bars appear; I see 3 of 4 or 4 of 4 bars in my house. Wait another moment, and EDGE data connection icon appears. Wait another moment, and the 3G icon appears, obscuring the EDGE icon. We are up and running with a good data connection, looking at the Setting up your T-Mobile G1 screen.
Press the MENU button, and the APN settings button appears. Tap it, and the APNs screen appears. Scroll to T-Mobile US and tap it. On the Edit access point screen, tap APN. Change the APN from epc.tmobile.com to internet2.voicestream.com
Tap Next. Scroll down to the Already have an account? section and tap Sign in. On the Welcome to T-Mobile G1 screen, type your Google username and password and tap Sign in. Wait a moment, and the next screen appears: Your Google account is now linked to this phone. Success! Tap Finish setup, and you're done. (Thanks to cash743 at modmyGphone for the clues.)
How fast is T-Mobile's 3G network on the G1? Let's find out. On the home screen, tap the browser. Type http://www.dslreports.com/mspeed into the address box and press the Enter key. Tap 100k and wait. The speed test reports that the download was too fast to take a measurement. Tap choose a larger file, and then 1MB. My result: 589 kbit/sec, 0.71s latency, 14.399s d/l time. Wow, that's fast!
Now configure your WiFi connection. Press the MENU button. Tap Settings, Wireless controls, Wi-Fi. The Wi-Fi check box turns green. Tap Wi-Fi settings, and the list of Wi-Fi networks appears. Tap your network. Type your key and tap Connect. Press the Home button, and you're done.
Have fun with your new G1.