Upgrading from G1, will plan have to change?

Pretty soon I'll either be buying the G2X or Samsung Galaxy S2, and I'm wondering whether or not I can get either of those phones on my existing plan which is the "T-Mobile Android Unlimited Web + 400 Messages". If I'll need to upgrade my plan, what should I expect to pay? What's the cheapest option?

Well I'm on the Android unlimited data (slows down after 5 GB :/ and I've been a customer since 2005), unlimited text and 1000 min free n/w. I pay around 80 dollars a month. I have the T-Mobile G2, so I could imagine the G2X is better.

But yeah expect to pay $80. Not a bad deal compared to FailT&T and Verizon.

When I bought my G2 over a year ago, they never asked me to swap my plans. I'm still on the $24.99 unlimited android plan. I have family plan messaging.

So safe to say, as long as it's an Android based phone you should be able to keep your data plan. Unless you switch over to Blackberry which uses it's on Data service (Don't quote me on this one)

You can keep that plan as long as it is a required feature. If you check your plan on the bill or on MY T-Mobile, see if the web feature has "REQ" next to it. If not, you will have to change to a newer plan if you do the upgrade because the system will need a REQ feature to be on there.

I too have a G1 and want to upgrade. I'm currently on a $59 family voice-only plan with the $20 Preferred Android Web data service. Looking at the upgrade to the Galaxy S II, it mentions this for the $50 Mail-in Rebate:
"Req’d for rebate card: 2-yr. contract extension with an Even More™ Talk + Text + Web plan OR Web service of at least $30/mo AND be eligible for full upgrade pricing."
Retail: $599.99
Discount: -$320.00
Rebate: -$50.00

Since my plan is not talk+text+web nor is my data at $30, does that mean I don't qualify for the rebate? If so, then the phone becomes $279.00 instead of $229.99. Or worse yet, will they automatically drop my $20 data plan and force me onto a $30 data plan?

And it looks like I don't even qualify for the upcoming Valentine's Day promotion since it requires a $99.98 family plan and the 5GB data plan. Technicalities aside, no idea if the 'Preferred Android Web' plan can be considered equivalent to the 5GB plan. I hate it when they rename a data plan, charge more for it, and then make the old-name data plans not work on new phones.

It is more of an issue of price point than what the actual feature is.  A $25 feature, even if it is a service equivalent, will not qualify for the rebate.

It is more of an issue of price point than what the actual feature is.  A $25 feature, even if it is a service equivalent, will not qualify for the rebate.

If losing out on a $50 rebate means not needing to pay $120 more per year for data, them I'm okay with that.

You can keep that plan as long as it is a required feature. If you check your plan on the bill or on MY T-Mobile, see if the web feature has "REQ" next to it. If not, you will have to change to a newer plan if you do the upgrade because the system will need a REQ feature to be on there.

There is a REQ version of the plan that he has.  He does not need to change.  They'll just add the REQ next to his plan name.

Does the REQ go away when my line is no longer under contract? Both I and my wife have the same Pref Android Web data plan on our lines but only her line has the REQ, though her line is still under contract. Does it make sense for me to call TMO and have them add the REQ to my data plan? Can customer service do that or do I need retentions?

When your upgrading on DISCONTINUED PLANS. The system will trigger that the DATA feature when upgrading needs to change. They will let you know and tell you that you must update the feature. DATA is required for every smartphone on contract. The system may originally refuse the upgrade unless it is changed. However, special departments can and sometimes are willing to override it.

With Preferred Internet. It may be tricky. However, it is a special feature and you probably could keep that.