Everything you need to know about T-Mobile's data-only plans

When is a phone not a phone? When you can't use it to place voice calls. Such a phone that's incapable of making calls sounds like an oxymoron. But it is not. T-Mobile offers a sharply discounted plan for consumers who want to use their smartphones only for data and text messages.T-Mobile's data-only plans costs $20 a month per line for 2GB of data, or $30 a month for 6GB of data — well below the $50 a month customers pay for a conventional T-Mobile plans with 2GB of data, plus v