Times Online claims that Nokia is planning on releasing a Windows Mobile 7 phone. A rumor has come up that a semi conduction company is making chips specified for a Windows Phone handset.
Take this with a grain of salt.
First of all, Nokia is working on upgrading its own OS system and therefore it would be weird for a Microsot OS to be placed on a Nokia phone. Some Microsoft Office features are coming to Nokia but a full mobile OS sounds hard to believe.
It could be a fluke and the semi-conductor company might be making LG or Dell phones.
Until I hear this from the horses mouth (or a leak happens), this is pure rumor.