Pulled the trigger and bought a Vibrant through Wirefly. I'm off contract and plan to use the data plan anyway so I opted for the discounted phone price. Here are some items that might be interesting to other folks that might be planning to get this phone.
1) Tmobile allows you to do an upgrade on only one phone if you have multiple lines on a family plan. Wirefly's online form doesn't allow this so they make you call their phone order line.
2) You can elect to keep the exact same phone plan you had before, but some resellers might not offer this option. Make sure to ask for it. In the case of Wirefly they had this option, but they tried to upsell me. I talked to 3 different agents as I worked out the details I wanted for my upgrade and one agent even said that it was not possible to keep the existing plan. It is but make sure to ask for it.
3) I had a data/message plan that I wanted to keep, Tmobile said they could transfer it to my new contract, but I had to purchase what the vendor had first then call them later to change it back. YMMV so check with Tmobile first, get them to add it to your account notes before buying the phone. It might be more difficult to get Tmobile to do it after you place an order. Note: I might have been able to pull this off because I had a G1 and an existing Android unlimited data plan to start with and was the same/better than the required $30 android unlimited package required as part of an upgrade.
4) Watch out for the fees. For an upgrade Tmobile charges an $18 upgrade fee. They will also charge you for shipping. At Wirefly I was told that I would be charged $36 activation fee. I told them that was more than what Tmobile said, but the Tmobile agent said that if that was the fee Wirefly was charging there was nothing they could do about it. The good news is that after I purchased the phone I followed up and the order fulfillment team said that they would only charge me the $18 upgrade fee.
5) Listen closely to the terms and conditions of the upgrade extension. Any changes to data or the plan will result in termination fees as well as additional charges by the reseller to recoup the phone discount. I think you need to keep the phone on the ordered line for 6 months or you loose the discount. Not sure it they can check and enforce this if you swap out sims.
Overall it was a painful experience with my having to call Tmobile and Wirefly multiple times to clarify specific items. Wirefly's phone sales really keeps on trying to upsell you as well as get you to buy phone insurance and accessories. Their call center in India can get really irritating (like a car dealership) when you don't go for their higher profit accessories and insurance. I especially hated their line "your getting an expensive ($200?) phone worth $600, why wouldn't you get insurance".
Final price is $149.99 + $18 upgrade fee + free standard fedex shipping and no sales tax to CA. This should be close to as good as it gets for an new release smartphone. Upsides are that I get to keep my old (cheaper) phone plan and unlimited data+400text plan ($10 savings per month). I also have the flexibility to upgrade my wife's phone at a later date.