NTT DoCoMo the official data provider for the 3G version PlayStation Vita announced the service end date. From March 31, 2017 you can’t use the prepaid data plan which costs 934 Yen (+ tax) / month.
It doesn’t means that you can’t use anymore the 3G service on your 3G / Wi-Fi version Vita. You can choose the Device Plus 300 and Flat-Rate Data Plan for the console from Docomo. Only the direct Vita data plan going to ends.