We already knew that Motorola's Droid RAZR Maxx was essentially the RAZR with a larger battery, but now it looks like the phones even use the same ROM. -Life took a look at the software of the two phones and found that they seemed identical, meaning that an OS update to one could probably be applied to the other. While it's not unusual for a company to put out multiple devices with similar hardware, there are usually minor software differences that require updates to be developed independently. Of course, using the same ROM also means there's a high likelihood the two phones are using the same antennas, chips, and other hardware.
A member of The Android Source forums took this knowledge a step further, reasoning that a leaked RAZR update from last week would run on the Maxx. According to an update on the post, the update installed successfully, opening the door for Maxx users to use any custom ROM developed for the RAZR. As always, putting custom builds on your phone carries some risk, but it looks like it might not be any greater than usual on the Maxx. And even for people with no interest in hacking their phones, identical software bodes well for the official Maxx update cycle.