Sensorly provides community powered mobile phone coverage maps. It is currently mapping 76 networks across the world. If you download either the Android or iPhone app you can also become a part of the crowd supplying data to these phone coverage maps.
You can use the Sensorly Google Maps to view how good network coverage is in a given location, for both WiFi and mobile phone networks. You can navigate to your part of the world by using the links beneath the map. You can also find the relevant map for your network from the tabbed buttons at the top of the map.
OpenSignalMaps is a great source for data about cell phone towers, cell phone signal strength readings, and Wi-Fi access points around the world. OpenSignalsMaps uses Google Maps to allow you to view the mobile signal strength for any location and view the locations of nearby towers for your carrier.
Using the map you can search by location and view a heat map of the signal strength for each of the carriers available in your area. You can select to view the data of individual carriers and quickly see how their local coverage compares. It is also possible to view the cell tower locations for each of your local mobile phone service providers.
The data for the map is collected from users of the OpenSignalsMaps Android application. Data from the downloaded apps is stripped of any identifying information.
Root Metrics allows you to compare the signal strength of different mobile phone carriers at different locations in the United States. You can search a Google Map by zip code or address to find the strength of coverage at any location.
The Root Metrics Google Map allows you to compare the signal strength of different mobile phone carriers. The map shows you each carrier's aggregate grade and the carrier's voice and data strength.
The Root Metrics iPhone app allows you to view the data from your mobile phone. Users of the app also contribute to the accuracy of the data shown. Data from downloaded apps is collected anonymously to track each carrier's performance.