...This build of Maemo is a fairly dramatic shift from past releases, having been largely rebuilt for the jump to phones.

The home screen (”Harmattan Direct UI”) is essentially one big vertically scrolling page on which users can add widgets.

We’ve seen a few widget examples so far, and they all appear to take up the full width of the screen.

These widgets are tightly tied to the rest of the phone.

Imagine, for example, that your home screen is made up of a calendar widget and a map widget, along with a handful of other widgets. If you make an appointment with one of your contacts, the appointment will automatically load into the calendar widget, place an icon in the right location on the map widget, and tie itself into any of the other widgets where appropriate

Home screen ad widgets would be tucked between these other widgets.

Unlike the other widgets, ad widgets would not be user removable or customizable.

The current plan is for Nokia to give control of these ad units to the carriers, presumably taking a cut of the ad revenue.

Nokia’s goal with these ad widgets is to make them incredibly context sensitive based on behavioral data. GPS placing you near a K-Mart? Bam! K-Mart ads. Browsing history showing you’re a peruser of Hello Kitty fansites? Sanrio ads might embarrass the hell out of you grace your homescreen.

Our source indicates that this is all part of Nokia’s larger goal of conquering the cell phone cloud services market.

Maemo Harmattan’s tentative release date is Q4 2010/Q1 2011.

Would carriers play along with this idea? Perhaps. While we were digging for independent confirmation of these details, another source pointed out that Pekka Ala-Pietilä, President of Nokia until 2005, left the company to start Blyk. As it just so happens, Blyk is a mobile operator in the Netherlands and UK which gives customers free texts/minutes each month in exchange for ad views. At the very least, this shows that there are carriers out there willing to experiment with the concept.