Although AT&T has had the iPhone 4 for almost a year longer than Verizon, the amount of iPhone 4 users on Verizon’s network is quickly catching up to AT&T’s market share. In fact, since launching on February of 2011, iPhone 4 users on the Verizon network now account for one-third of the iPhone 4 subscribers in the United States. For comparison’s sake, the AT&T model was launched in June of 2010, giving AT&T an eight month head start.

That gap is now steadily decreasing, according to a report by Localytics. Their findings reveal that, after starting out with something of a crawl, iPhone 4 uptake on the Verizon network has seen a noticeable increase during the summer months. Are more people abandoning AT&T for their competitor, or is this simply a case of Verizon users catching up to the AT&T plateau? In other words, do most AT&T users who want(ed) an iPhone 4 already have theirs, while the Verizon users are still in the process of acquiring theirs, or is there something else to consider?

From Localytics perspective, Verizon’s unlimited network gets some credit, but now that Verizon’s network is going down the misguided limited route, will that change the desireability of their iPhone 4?

Why the recent uptick in Verizon adoption? One reason may be Verizon’s unlimited data plan, which they are scheduled to do away with on July 7th. AT&T officially discontinued its unlimited data plan in mid-2010, although existing customers were allowed to keep their plan as long as they remained AT&T customers. We’ll continue tracking the shift in iPhone 4 market share to see if Verizon loses momentum post-unlimited-data.

There are graphs included in the Localytics study, which do a great job of demonstrating the shift in market share:

As you can see, the summer months have been very good to Verizon and their version of the iPhone 4. Too bad something has these mobile providers convinced that a tiered, limited mobile web is wise and just strategy. Must be the money.

Those of you desiring the iPhone 5, do you think you’ll get yours through the AT&T or Verizon? Let us know what you think.