900 Mhz equipment is probably located in the license-free band. Assuming it is FCC compliant you shouldn't need a permit for installation as it's no different than a cordless phone or a WiFi router. There are still restrictions on transmission power even though there isn't licensing in place.
The reason most consumer wireless uses 900 Mhz, 2.4 Ghz, and 5.2/5.3/5.8 GHz is because they're all unlicensed frequencies. 24 GHz and above 60 GHz are also unlicensed.
2.4 Ghz is near the resonance of water molecules.
60 Ghz is near the resonance of oxygen molecules.
"The Doppler effect means red lights will appear to be green if you drive fast enough..."
1) Wait for disaster 2) Determine it's not your fault 3) Blackmail the culprit 4) Profit
Caution: Classless when exhausted from a tough day at work, may attempt to compensate with poor humor and Christmas cheer...