iPhone users resist the lure of Sprint’s unlimited plans

Sprint’s(s s) unlimited data plans don’t seem to be as big a draw as it had hoped when it comes to selling the iPhone(s aapl). Sprint sold 1.5 million iPhone 4 and 4S handsets in the first quarter, compared to the 3.2 million Verizon(s vz)(s vod) and 4.3 million AT&T(s t) activated in the same period.

Given Sprint’s size – with 56 million total connections it’s about half the size of either Verizon or AT&T – 1.5 million iPhones certainly isn’t a bad haul, but it certainly doesn’t indicate customers are flocking to the carrier lured by cheap data. Part of the problem is that the pickings were already slim when Sprint first started selling the device in October. AT&T and Verizon had already locked a good deal of customers into contracts, and AT&T in particular has been aggressively upgrading its older iPhone customers to the new 4S and to new 2-year contracts.

Though the iPhone may not be a runaway success for Sprint, it’s managed to use the device both to keep its current subscribers happy as well as bring in new customers. Sprint said 44 percent of its first quarter activations were new accounts, so it’s not merely recycling its old customer base, swapping out Android(s goog) phones for iPhones. And even if AT&T and Verizon are far outpacing it in iPhone activations, Sprint is quickly becoming a significant part of Apple’s smartphone empire, accounting for 4 percent of Apple’s global 35.1 million global iPhone sales last quarter.

The iPhone also contributed to Sprint’s more than 1 million net subscriber additions. Most of those customers came from its wholesale business – connections it sells to mobile virtual network operators and Sprint’s regional affiliates – and its numerous prepaid brands, but Sprint managed to grow its core CDMA contract subscriber base by 263,000, which offset a loss 455,000 Nextel iDEN customers.