(1) If you get the $20/mo wi-fi addon, does that cover all devices, i.e. I have a cell, an iTouch and a laptop? Does wifi fee cover TMo hotspots outside USA?
The T-Mobile $20 hotspot add on covers all devices but you can only log on one at a time at a T-Mobile hotspot. It's usually $20 for the hotspot service and $20 for EDGE (Internet over the phone network)
(2) Does the wi-fi fee cover internet surfing from your cell, or is that another $5.99?
If your cell phone has wifi you can connect to any wifi network you want. You only have to pay for it if the wifi network charges you. Like I said above T-Mobile will let you access their airport/starbucks hotspot service for about $20.00 a month. The $5.99 is T-Mobile web which lets you browse limited websites on your phone itself. That has nothing to do with wifi.
(3) What about blackberry (push email) service? Is that another add-on? (at sprint it is $40/mo!)
Yes - it's $20 a month for a personal (unless you get the corporate version)
so your basic data choices on T-Mobile are:
$20 - phone Internet (Blackberry Internet push, Windows mobile data, etc any smartphone with Internet/email)
$5.99 - Phone Internet for any non-smart phone. For any smartphone you get the $20 phone Internet plan instead.
$20.00 - add on to get T-Mobile hotspot service so you can use a laptop or any wifi device to jump on a T-Mobile hotpsot.
$20.00 - add on to get Hotspot@Home service. This gives you unlimited calls over the Internet for free if your phone supports it. Only a few phones support it. The only decent phone is the Blackberry Curve.
(4) What happens when you are roaming overseas? Is it 99cents/min for (a) incoming calls from USA (b) Outgoing to USA from Europe? (c) cellphone to cellphone within Europe?
$0.99 to and from the US when roaming in Europe. Other countries have different rates. T-mobile will unlock your phone so you can buy a prepaid SIM.
(5) Any good promos we should watch for (e.g. $10/mo wifi, 1000minute deals, etc.)
I don't know...maybe check out wirefly.com or Howardfourms.com
Would also appreciate any thoughts on coverage within California.
I have had no issues with T-Mobile around San Jose (mostly hang around Great American Parkway), all over San Fransisco, and Orange County / Anaheim area. No issues I can remember when I was in San Jose either. I go to those area quite frequently and no issues with AT&T or T-Mobile.