These are essentially the same as mobile phones, except stationary and with the possibility of installing an external antenna. They use SIM cards and connect to the GSM network same as a normal mobile phone. In many cases, especially at the extreme limits of coverage of an existing GSM networks, these phone are connected to high-gain directional antennas. When a community network is installed close by, the receiver on these fixed wireless terminals can be "deafened" due to the very high gain antenna and the relatively high power of the newly installed signal, which means the phone no longer is able to receive the signal it once did from afar, even if the two networks are on different frequencies. The same thing can happen with repeaters. In Mexico, this problem is most common with Telcel fixed wireless terminals.