A BusinessWeek blog claims Apple is set to miss its end-of-February deadline to release the promised software development kit (SDK) for the iPhone by as long as three weeks.

The blog by Arik Hesseldahl cites an unnamed source who said the SDK will be late, although no reason was given. Other bloggers have written they've heard rumours of a mid-March release.

An Apple spokeswoman said the company does not comment on rumours or speculation.

Apple CEO Steve Jobs posted an open letter in October that the SDK would be released in February. The letter came as a turnabout, after Jobs had defended Apple's decision to forego an SDK on security grounds.

As with other nuances of the iPhone, the SDK's release, as well as its release date, are followed closely by Apple observers and fans of the company's products. Various blogs in January posted purported leaks of the SDK key. FierceDeveloper in January cited Austin.Heap.com and Zibri's Blog, and the alleged key.

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