[yyao]

The question of receiving signals is more a philosophical one of ethics. The question of broadcasting signals is one governed by law. In North America, you can't broadcast on a part of the spectrum that you don't have a licence for. Wifi devices, 900MHz phones and CB radios and such operate in a frequency band which has special provisions for such use.

I looked at their product specification and there isn't any mention of phase noise of the local oscillator. It turns out that a critical requirement for tuning into GSM signals is the phase noise or jitter of the local oscillator. Chances are, they are using a pretty good cystal, but probably not good enough for a GSM base station.

There is a good reason why GSM base stations all run off rubidium standards. In fact, you can grab 10MHz rubidium standards for a very (relatively) cheap price off eBay. They are all from decommissioned cell towers.

There is a possibility that you can still tune into a GSM signal with a substandard local oscillator. However, this behaviour would be intermittent.