[Nexus One General] maxawesome:
This knowledge comes after talking to 5 different T-Mobile reps.

The steps to get the subisidized price if you are a 22+ month "good standing" customer with a Family Plan of any kind (legacy, myFaves, Even More, etc):

If you have a Family Plan (myFaves, Even More, etc.) you *must* split all the lines on the Family Plan off to individual Even More plans. T-Mobile doesn't allow one person to have multiple types of lines on the same account, and doesn't allow one person to have multiple accounts.

Wait 2-3** hours for Google's system to replicate account data from T-Mobile. **estimated

Now that all your lines are on individual plans, you can use the steps on Google's site to modify an existing individual plan and then upgrade your phone.

Once you have received and activated your new phone on your existing number, it will convert your plan to the $80/mo Even More plan.

At this point you can call T-Mobile and have them add all your lines to an Even More Family Plan (not the Even More Plus Family Plan).

And if all this fails, she gave me HTC's support phone number: 888-216-4736

UPDATE: It appears I was a bit hasty in writing my guide. The steps above actually lead you to be able to upgrade your existing line with a $150 discount on the Nexus One, dropping the price from $529 to $379. To get the $179 pricing, you must select "Add a new individual line of service with a new number to my T-Mobile account." This will add a new line to your T-Mobile account, which you can then add back to your Family Plan, and remove your old line.

UPDATE #2: Google is now issuing a $100 refund if you went through this process and bought the Nexus One using the "upgrade" option for an individual plan to get the price of $379. That brings your cost to $279. I thought Google folks were supposedly good at math? :O

UPDATE #3: After all this nonsense, I found out today from T-Mobile that step #5 DOES NOT WORK the way they told me it would. You can't just call them and have them add all your lines to a Family Plan. Doing so within 120 days of your Nexus purchase will cause you to pay an ETF to Google, equal to the price difference between the $179 price and the $529 price.

My journey:

I started with 3 lines on a MyFaves 1200 Family Plan and was paying about $190-200 a month. I split this into 3 Even More 500 lines with Android data on 2 of the lines (my wife inherited my G1). Total cost per month at this point was roughly $200 still ($49.99 x 3 plus tax). I then bought the Nexus One for $179 ($229 with tax), which added a 4th Even More line for another $80/mo. Total cost per month now at $280ish.

Now, at this point I could have cancelled one of my out-of-contract lines, saving $49.99/mo for that line, dropping the monthly down to about $240/mo for my 2 old lines + the 1 new line from Google (3 lines total).

Instead, I cancelled the Google line, dropping the monthly back down to $200/mo, retaining out-of-contract status on all 3 lines, and eating the $350 that Google will charge me now. Had I kept their line for another 120 days though, that's 4x$40=$160 to keep that subsidized price, plus I am committed for another 2 years. At the same time, we are now signed up for the Even More Family 1500 plan with unlimited text/data/tmo-to-tmo/nights&weekends.

So at this point, I have the option (if I can explain all this math to my wife), of just buying her an unsubsidized phone upgrade for her and the other person on our plan, and drop to an Even More Plus 1500 Family Plan, which would cost us $125+tax/mo, for a total of about $150/mo. So basically in a year's time, we will have saved $600 on our phone bill, and that will buy each of them a very nice phone. Wish me luck explaining this to her.

Sorry to get everyone's hopes up. I think Google has shown that they can f*ck things up as bad as any big company out there (at least on a first try). Hopefully they will learn from it, and/or HTC will get into direct handset sales instead (like they should have this time anyways).

MORAL OF THE STORY: Save your pennies and just buy the effing thing unsubsidized. That or don't have family. Your choice. :)