Japan will be among the first batch of countries to receive Apple Inc.’s new iPhone 5 when it launches on Sept. 21, but will it be missing a key selling point?

While the new smartphone will be available for two Japanese carriers KDDI Corp 9433.TO +1.07%. and Softbank Corp 9984.TO -0.91%. when it goes on sale next Friday, there’s one small hitch: neither carrier currently operates the high-speed mobile network — known as Long-Term Evolution — which is compatible with the new iPhone.

If the networks aren’t up and running by then, the new iPhone may be without one of its key selling points: the ability to access data at faster connection speeds.

Nonetheless, that may do little to quell enthusiasm for a new iPhone in Japan where it is the most popular smartphone and long lines accompany the debut of any new Apple product. Also, the absence of a compatible LTE network didn’t prevent Softbank from selling the latest iPad earlier this year.

Softbank and KDDI have announced that they plan to roll out a LTE network compatible with Apple’s products sometime this fall — although both companies declined to say whether the new network will be available by Sept. 21.

Softbank already runs a high-speed LTE network using a different standard, but it has said it plans to debut a FDD-LTE network — the one that works with the iPhone 5 — in autumn 2012. KDDI had originally said it would roll out its LTE network by the end of 2012, but it pushed forward those projections to fall of 2012.

Both companies said they plan to offer more details about their LTE plans in the coming days.

NTT DoCoMo 9437.TO 0.00%, Japan’s largest mobile carrier, already operates a LTE network compatible with the iPhone 5, but it does not offer the iPhone among its handsets.