If it is a 4G device in particular, I will assume the answer is no, because there are customers that have the older broadband cards that were grandfathered when the upgraded to another 3G BB card, Mifi, or 5 Spot, however when they upgrade to a 4G BB card or 4G Mobile Hotspot device, the system tells us that the current plan is not compatible with the device.
For that reason, I doubt very seriously that the unlimited plan will be grandfathered for 4G phones that are to be activated on a line, regardless of how it was purchased.
That of course begs the question as to whether or not that translates to if you get another 3G device after July 7th you will be grandfathered, but believe it or not, at the retail level the info we have access to up to this moment has not gotten into that much detail, even though we are fielding questions on this left and right. TBV