SlashGear writes, T-Mobile Monthly4G customers rejoice; the carrier will be launching an unlimited 4G data plan on January 9th. The prepaid plan will be priced at $70 a month, and will provide the first 5GB of data at 4G speeds. This is a jump from the current $60 plan, which offers 2GB of data at 4G speeds, with it dropping down to 3G speeds after the cap is reached. Says T-Mobile, the plan is “perfect for video chat, streaming music/movies/TV and playing online games.” Of course, the plan comes sans-contract, one of its most alluring features. In addition to the unlimited data and 5GB at 4G speeds, the…