Ahead of what is strongly tipped to be the launch pad for the 3G iPhone - Steve Jobs' keynote at WWDC08 on Monday - Microsoft has issued a letter to industry partners that appears to rally support for their rival smartphone platform, stating: "more and more competitors are jumping into the smartphone market or announcing upgrades, with features we delivered to customers years ago".

With barely veiled references to Apple's mobile phone offering, Andy Lees senior vice president, mobile communications business, Microsoft, states that nearly 20 million Window Mobile-based licenses will sell this year and that "in the last quarter our year-over-year unit growth alone was greater than sales of Apple's iPhone".

Lees states that the Windows platform gives: "the freedom for people across the globe to get the type of handset they want on the network they want, the flexibility for our hardware and mobile operator partners to build on the platform, and the opportunity for developers to create applications on our platform for virtually any need".

Addressing Microsoft's Windows Mobile partners, Lees says: "You've delivered Windows Mobile phones with features like GPS, 3+ megapixel cameras, and voice activation - features that other operating systems have been slow to deliver".

In addition, the letter states that together they offer: "more than 40 different phones that run at 3G speeds, at prices that meet a range of customer needs - something not all smartphones can claim".

The fact this letter has been sent at the time it has (two working days before the Apple event) suggests Microsoft is not planning a competitive response to the 3G iPhone - but wants to give partners a reassuring pat on the back before the hype for next week's Apple announcement really kicks in.