Motorola’s and Verizon Wireless’ $100 million marketing campaign for the Motorola Droid seems to be paying off with strong sales that will likely result in more than 1 million devices being sold by the end of the year.

The Droid, the only smartphone currently on the market that uses Google Android’s 2.0 operating system, is Motorola’s second Android device and it’s available only on Verizon Wireless’s network. The device is turning out to be the hit phone of the season, thanks in large part to an expensive and extensive advertising campaign.

Neither company is reporting sales figures. But analysts say sales look good. The companies have likely sold between 700,000 and 800,000 Droids since the device was launched in early November, according to equity analyst Mark Sue of RBC Capital Markets.

“Verizon’s big marketing push for the Droid is strengthening as we close in on the holidays, and following our round of checks, we believe about 700,000 to 800,000 Droids have been sold, making our hurdle of 1 [million] Motorola Droids achievable for 4Q09 [ending December 31],” Sue said in his research note. “Motorola, for its part, has done a good job on the production side, and our survey of over 100 stores indicates strong demand, limited stock outs, and very few returns.”

John Stratton, executive vice president and chief marketing officer for Verizon Wireless, said when the device was launched in late October that Verizon would be pouring in more money to market this device than any other phone it has ever sold. And now it looks like the money has been well spent. From advertisements that specifically highlight the Droid to ones that focus on Verizon’s extensive and reliable 3G wireless network, it’s clear that the company has AT&T and the Apple iPhone in its crosshairs.

AT&T has actually sued Verizon over the advertisements about its 3G wireless network coverage.