Japan's top carrier NTT DoCoMo (NYSE: DCM) has never offered Apple's (AAPL 1.27%) iPhone, and that's not about to change anytime soon. NTT DoCoMo exec Kazuto Tsubouchi recently compared the device to DisneyLand, using the theme park as a comparison for a walled garden. The carrier would prefer to have more control over the experience, something that Apple isn't willing to give up.

CEO Kaoru Kato is echoed these sentiments in a recent interview with Reuters. The executive said that NTT DoCoMo wants to "develop a lifestyle system," and that Apple's controlling ways have an adverse " impact on the services" that the carrier offers. That's why the carrier has been aggressively marketing two rival Android devices from Samsung and Sony, the Galaxy S4 and Xperia A. NTT DoCoMo has reportedly sold 830,000 Xperia A units since launch, but the Galaxy S4 has moved less than half that.

The iPhone's absence continues to hurt NTT DoCoMo's subscriber base, and the company has lost an estimated 3.2 million users over the past few years as a result. Smaller carriers Softbank and KDDI have been more than happy to welcome iPhone users. NTT DoCoMo's various service offerings are becoming less relevant as viable alternatives that are easier to use have surfaced in recent years. NTT DoCoMo may not be able to withstand the pressure much longer on the strength of its services alone.

If the carrier continues to bleed customers to Softbank and KDDI, BNP Paribas analyst Hiroshi Yamashina believes that NTT DoCoMo will have no choice but to partner with Apple eventually, even if that entails strict requirements and hefty subsidies.

Apple has plenty of opportunity with new carrier partnerships. The company's total number of iPhone carriers hasn't budged in any meaningful way in years, hovering around 240 currently. Partnering with new carriers allow the iPhone maker to tap the pent-up demand within new customer bases from those who want an iPhone but aren't willing to make the switch. One of these days, NTT DoCoMo will have to come around.