The previous information coming from Motorola was that you wouldn't receive the LTE update if you have unlocked your Motorola XOOM. Now, however, it turns out this is not true and all Motorola XOOMs will be eligible for the LTE upgrade.
Mind that the manufacturer kindly requests that you send the tablet with the factory settings intact, but even if you send it rooted, Motorola will still install the hardware upgrade. However, it may be unable to install the software update, which sounds fare to us.
The Motorola XOOM LTE upgrade is set to arrive in Q2 of 2011, and more info about the process will be made available prior to the upgrade's arrival.
source: Motorola Support Forums via Engadget