With 7.4 million Lumias sold last quarter, at $25 per Windows Phone license, Nokia is drawing just $70 million each quarter from Microsoft. At 10 million units, they'd start paying Microsoft money.
Blackberry sold 6.8 million units last quarter. They have no maps to license to Microsoft. If they signed an agreement with Microsoft tomorrow, it'd still take several months for the first handset to come out. What would Blackberry be worth to Microsoft in a year?
The numbers are not in Blackberry's favor. That having been said, I will never underestimate Steve Ballmer's ability to overpay for a deal.