Re: [GUIDE] Don't Panic: The Hitchhiker's Guide to the Galaxy Nex
You can most definitely do this. You'll want to prevent the battery drain, connection attempts, and failed authorizations that come with not having an LTE SIM. Simply turn off LTE (it's under the mobile network type; you want "CDMA Only"). This setting should persist through a power cycle, meaning you don't have to reset it each time the device boots up. Now, taking this one step further to a WiFi only device wouldn't be hard. Simply turn off mobile data networks, or, if available, a "None" option under the 'mobile network type' setting.
Just a side note for those using custom ROMs: this is the reason that the LTE toggles in the notifications bar will usually not reset when the phone boots (at least they haven't in my experience). They change the mobile network type, which is a persistent system setting.
Edit: there is also a way to prevent the automatic activation service from getting in your way, but I'll have to look around a bit to find it.