UK cellco Vodafone added the third prong to its three platform handset strategy on Monday, cutting a deal with Microsoft for the development of Windows Mobile devices.

The deal forms part of Vodafone’s wider strategy of streamlining its platform portfolio to deliver greater cost efficiencies across the group. Over the next five years, Vodafone expects to standardise on three mobile operating system platforms: Microsoft Windows Mobile, Symbian/S60 and Linux.

The first device to use the software produced under the agreement is planned to be with Samsung and is expected to launch in the first half of 2007.

Analyst Dean Bubley of Disruptive Analysis likens the Vodafone strategy to NTT DoCoMo’s approach in Japan, which is based on its own flavour of Symbian OS, as well as Linux and Windows Mobile.

But Bubley questions the rigidity of the strategy when considered alongside the various handset manufacturer roadmaps.

Obviously Nokia S60 devices will fit in happily, but the question remains as to where the S40 platform, used by Nokia’s mass market devices, will go. Perhaps the S40 is replaced by S60 as the flagship operating platform shifts downmarket, or maybe Nokia persuades Vodafone it needs special dispensation as a market leader, Bubley said.

Motorola meanwhile is likely to shift its mid and high end devices to Linux, with a few Microsoft powered phones thrown in at the top. But again, Vodafone may need to be flexible if Motorola hits upon another runaway success with a low end, embedded OS phone like the RAZR.

Sony Ericsson is another vendor that is fond of its embedded OS’ as well as the UIQ platform. Given the company’s acquisition of UIQ on Tuesday and the success of the W950 Walkman and P990 phones, it remains to be seen whether Sony Ericsson will receive dispensation as well.

Korean vendors Samsung and LG Electronics, both known for their promiscuous ‘build a device based on any platform’ attitude are likely to find some way to fit in nicely, as will Taiwanese Windows Mobile shop HTC.

But Canadian BlackBerry vendor Research In Motion (RIM) looks like it might be in trouble, with no room in Vodafone’s strategy for RIM’s own platform.

Disruptive Analysis’ Bubley also raised another interesting point regarding the question of what sits on the top of all these operating systems. “Will it be a proprietary Vodafone IMS plus other stuff client? Will it be a third party layer like Flash? Or will it vary between targeted customer segments?” he said.

Wild speculation at telecoms.com suggests that Java darling SavaJe, currently missing in action, might even be in with a chance here. There is obviously something amiss at the company as neither the management nor the backers will speak at the moment, with the smart money being on financial difficulties.

But telecoms.com has seen an as yet unannounced, ready built Vodafone Live! interface based on the SavaJe platform, which could be rolled out across its three prong strategy. As Vodafone is already an investor in SavaJe, maybe the operator could assimilate the company or at least the technology.