This is what Cingular is saying, because they are lumping all phones that have a 'keyboard' together. regardless of the OS it is running. It will work fine on the MM200, or the SM plan.
of note with the rebate, if you read the rebate requirements, it doesn't say which plan it requires. It just says unlimited data plan.
Many have been on this plan and gotten rebates in the past. Just an FYI - remember, tho, that YMMV!
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Ricoks
Currently -> Cingular 2125
Previously -> Audiovox SMT5600, Motorola MPX220