In the months leading up to Apple’s iPhone 4S announcement, the rumor mill had T-Mobile pegged as getting the handset. And with the country’s number three carrier slated to receive the device, it made sense that number 4 would as well.

But on October 4, when Apple unveiled its latest smartphone, there was no mention of the operator. It isn’t that T-Mobile isn’t interested in carrying the smartphone, it’s that Apple has yet to extend the offer. And the carrier will bleed customers because of it…

According to AllThingsD, T-Mobile said that it would likely see an increase in customer churn in Q4 of this year. The forecast came during the company’s quarterly earnings call yesterday afternoon, and was attributed to the fact that it still doesn’t offer the iPhone.

Although its number of new subscribers in Q3 was only down 10,000 year over year, that total is expected to increase over the holiday quarter. It makes sense, considering the number of T-Mobile customers that likely stuck around based on rumors of it getting the iPhone.

Not carrying Apple’s handset isn’t its only problem. Customers are also leery of the current AT&T buyout situation, and what that could mean for pricing plans and service. There’s something unappealing about a carrier in a “transitional” stage.

But with Sprint now an iPhone partner, T-Mobile is the only company out of the top 4 US carriers that doesn’t offer the popular device. T-Mobile is in for a bumpy fourth quarter.