AT&T customers who've managed to hold strong to their $30 unlimited data plans since the carrier ended that option back in 2010 are about to get a bit of a surprise. According to 9to5 Mac, AT&T is seeking to increase that $30 a month fee to $35 a month (CNBC and CNET have also corroborated this story). That isn't much of a jump, but it is the first price increase of the grandfathered plan in years. Still, AT&T is hardly the only culprit here. T-Mobile has increased its unlimited data plan from $80 to $95 a month, Sprint is now charging $70 a month for the same thing and Verizon has upped its own grandfathered unlimited data plan by $20 a month. The unlimited data price increase for AT&T customers will go into effect in February of next year.