How far can 3G cover?

Typically You get around 5 miles from the tower, though theoretically a gsm tower can broadcast up to 20 miles . There are also cell repeaters that can extend useful range to around 15 miles or so. I have heard reports of longer range, but 15 seems like a reasonable expectation.

Read more

What does Opensignal app do?

CrisisSignal is an Android app to identify the status of communication networks (and outages) in emergency response areas . The interface is a real-time dashboard of signal strength, available networks, and other metrics. It has been used to assist with the relief efforts in Ebola affected regions.

Read more