Apple is understood to have unleashed its lawyers over the weekend, targeting mobile developer sites posting details on how to hack handsets to look like the iPhone.

In the wake of Apple’s unveiling of the device, a number of websites catering to the developer community have published files and instructions on how to modify the user interface of Windows Mobile and Palm devices to look like the iPhone.

The website xda-developers.com was one of the first to publish the skins and has since posted a message asking users to refrain fro posting material that “Apple may view as copyrighted”.

Mobile news site MoDaCo was also contacted by Apple’s San Francisco-based lawyers, O’Melveny & Myers, for linking to and posting screenshots of the skins. The legal note warns that “the icons and screenshot displayed.are copyrighted by Apple” and as such cannot be displayed.

It has only been in the public eye for a week now, but Apple is already no stranger to legal wrangling over the iPhone.

The company is in hot water with networking giant Cisco, which owns the “iPhone” trademark in the US. Cisco filed suit against Apple last week for alleged trademark infringement.

In a new twist it has also emerged that Citrix may be gunning for the Californian company over its use of the phrase “Visual Voicemail”. The Apple iPhone contains a feature which allows access to voicemail via a graphical interface, meaning users can view their messages and jump straight to a particular one, rather than listening to them in order.

Citrix’s Voice Office applications suite for IP phone networks also features Visual Voicemail, which does exactly the same thing.

We were unable to turn up any such trademarks on the US Patent and Trademark Office website, although a brochure for Visual Voicemail, as provided by Citrix, claims “Visual Voicemail” is a registered trademark.