Short answer: Yes it will work, but only phone calls & text messages will work. Web browsing, email or IM won't work without a data connection. Also, the phone won't be able to use the Android Market.
It won't really be necessary to disable any settings, however you can reference this for more information about the settings on the myTouch 3G Slide.
I can confirm from a week of experience that the MyTouch 3G Slide will work without a dataplan. I had to call customer service to block pay-as-you go data, so that I wouldn't be charged if I accidentally browsed to a web site, etc.
Also, I *am* able to web browse, email, and use the Android Market when I am using the Wi-Fi connection. Woo hoo!
I've been successfully using GMail and Evernote, and the apps only sync when I'm connected to Wi-Fi. So it's been pretty great!
Can you please update your answer to include that web browsing, email, Android Market can be used with Wi-Fi if a user has no data plan?
As a T-Mobile employee with the "T-Force" user rank, I feel it's important that you update your answer with complete information as it becomes know.
Hello there adamporad,
Currently, only the items mentioned above, phone calls, text messages are supported by T-Mobile when you don't have a data plan on the MyTouch 3G Slide.
It's probable that you can get data related functions working on a WiFi network, but T-Mobile cannot support those functions with no data plan.
In other words, we don't do anything to disable those items, but cannot offer assistance if you have trouble using them on WiFi with no data plan.
Of course, there's lots of nice people in these forums who may be able to offer insight or guidance in that event.