Anyhow, the basic idea is that students work competitively in pairs or groups to answer a list of questions with two choices, each choice having a number attached to it. Here are a first few examples from the activity I did:
1. The government are trying to implement (0)/activate a law (1) to ban smoking
2. You will get better at English if you use a variety of effective study (8)/learning (7) strategies
I've done this a few times with different groups, and they absolutely love it. Just the competitive element plus the technology part really motivates them.
I'm not sure if this is technically using your mobile phone for language learning, but it's certainly a good activity to do and that's why I've included it here.