Apple today said that white models of the iPhone 4 won’t be available until “later this year.”

According to a statement from the company, the white models “have continued to be more challenging to manufacture” than originally expected. The company said this will not affect production of the black models.

A note published by UBS Investment Research this morning called the delay of the white iPhone 4 a “net neutral,” noting that Apple’s management probably did not embed sales of the white models into their financial projections given the ongoing manufacturing challenges.

UBS said that regardless of the white iPhone 4 delays, it still expects Apple’s broad portfolio (particularly iPad and iPhone) to be two of the most sought-after products into the second half of the year, in particular, the holiday season, which will translate into continued growth momentum.

The iPhone 4 has been plagued with problems surrounding the device’s exterior antenna, which critics say loses signal when users touch the lower lefthand portion of the phone with their hand. As a result, Apple has agreed to provide free cases or “bumpers” to remedy that problem. Starting today, users can download an app to their iPhone via the App Store and that will allow them to select their free case.