The following are the cell requirements for normal MS cell camping (ref 1):
The handset's decision to camp to a BTS is made in the handset. The
BTS can send signals that can encourage a handset to behave one way or
another, but in the end the BTS cannot force a handset to camp,
The handset will camp to whatever network its SIM is programmed to prefer, which is usually the network of the operator that issued the SIM, followed by its roaming partners. (A locked phone is one that will only accept SIMs from the carrier that locked it.) The only way sure to get the MS to camp to your BTS automatically is to be the only BTS available. Here are four ways to do that:
Note that we DO NOT RECOMMEND using the network
parameters from your local network and relying on proximity to the test
BTS to get a phone to camp to it. First, that is much less reliable
than the options
Camping depends heavily on a number of factors. Once a handset has registered with a network, it usually is quite happy to stay there until something prompts a change. In most cases, if you are using an operator's SIM, say AT&T, the handset will stay on the current network until its current connection quality drops, it moves, or it sees another AT&T signal or another signal in the SIM cards preferred provider list. Your BTS then either needs to be broadcasting the same NMC/MCC (i.e. spoofing...which has legal implications) or you need your own SIM card in the handset that is configured with the MCC/MNC of your BTS.
The other way to accomplish this is to set your OpenBTS to use the 001 test code for MNC. Most
phones will attempt to camp on this code if its the best signal around
and its not happy on its own network. This
In the end, unless you use your own SIM cards and you have the phone configured to use your BTS, it won't just jump over to you if its happy where it is....and certainly for operator SIM cards, the phone will keep to its preferred provider list. You should also be aware that if the phone is SIM locked then you can't even put your own SIM card in the device as it will only work with the network that locked it (i.e. if you have an ATT phone and its been locked to only use the ATT network, then it won't work at all when you change the SIM card).
注：MS Camping Conditions（原文出处，翻译整理仅供参考!）