The iPhone 6 Plus has an Achilles heel

The iPhone 6 Plus is a fantastic phone with an unfortunate flaw: It's a data hog.

iPhone 6 Plus users consume twice as much data as iPhone 6 users, according to a Citrix report.

That's because people are using the 6 Plus like they would a tablet, watching tons of video and playing games.

Citrix says iPhone 3GS users consume about a tenth of the data as 6 Plus users, though we're not sure how many people are still using the older, five-year-old handset.

Citrix's data shows how owning an iPhone 6 Plus can be a lot more expensive than an iPhone 6 over the long-term.

My data plan on AT&T, for example, would cost $360 more per year if I doubled my consumption. That's more than half the cost of buying a 16GB iPhone 6 outright, without a contract.

High-speed LTE cell networks are also enabling smartphone users to stream video like never before. Netflix steams one video for every 4 YouTube videos over LTE networks, according to Citrix. On 3G networks, the ratio is one Netflix video for every 7 YouTube videos.