Microsoft may be forced to make a big purchase after Google's deal to buy Motorola Mobility.

There has been a lot of speculation about what Google’s purchase of Motorola Mobility will mean for the industry as a whole, and especially Microsoft.

It’s no secret – sales of Windows Phone 7 haven’t been all that impressive. Android is still the leader in the mobile space and probably will be for the foreseeable future.

What does Google’s purchase mean? Motorola was the top manufacturer of Android devices until Samsung took over the lead late last year. The Wall Street Journal reports (subscription required) that the deal could help WP7 sales – other manufacturers (Samsung, HTC, etc.) will now compete against Google-owned Motorola. Will they jump ship to another operating system?

Here are some more thoughts on the deal:

Patents: Microsoft has been chipping away at the Android platform with numerous patent deals, where manufacturers pay Microsoft a royalty for each device sold. Last month, Microsoft, Apple and Research in Motion acquired Nortel’s patents for $4.5 billion. That deal is currently under investigation.

Google was interested in buying Motorola’s patent portfolio, in part to stave off patent lawsuits against Android. Why not buy the whole company?

A manufacturer fully in Google’s court: It would be pretty tough for the folks at Motorola to start selling webOS or Windows Phone devices. At the end of the day, they are now owned by Google and will make devices based on the Google-developed Android operating system. Nokia agreed to manufacture smartphones loaded exclusively with Microsoft’s Windows Phone 7 OS, Google basically did the same thing, except now they own a manufacturer.

Motorola is still in second place in the Android manufacturer race (HTC has 35 percent of the market), but now Google can do anything they want with their own manufacturer.

Force Microsoft to buy a device manufacturer: TechCrunch has an interesting perspective – the deal might make Microsoft buy a manufacturer. Motorola has recently restructured, and the mobility division was spun off from the rest of the company. Motorola was probably the most enticing buy, but would Microsoft now be forced to buy a manufacturer (Nokia would make sense, but Research in Motion has also been mentioned) in order to compete?

Of course, everything is just speculation now. It’s going to take awhile to see what it all means, and if Microsoft goes through and buys a device manufacturer. The stock prices of the companies involved might be the most interesting sign (at the closing bell at 1 p.m. PST):

Google (NASDAQ:GOOG): down 1.09 percent, Motorola Mobility (NYSE:MMI) up 55.82 percent, Microsoft (NASDAQ:MSFT) up 1.63 percent, Tech sector: up 1.69 percent.