Well, and 2 TB of key tables.
Not to mention the fact that since it's just a simple look-up table with lots of small entries, you could store it in the cloud and only get what you need via the same GSM connection.
I wasn't saying it wasn't doable, but rather it's not just as easy as grabbing your laptop and a $15 phone, which is how it's being reported, for the most part.
And they have furthermore been modified to remove filters that in "normal" phones improve signal reception but for this particular application would prohibit you from listening to the base-station-to-phone direction.
And only one single of those was modified (the one used to dump the traffic/voice channel, the other only listen to the BTS)