Sure, you can use Android instead of Windows Phone 7, but you still have to pay up.
Microsoft doesn't think so, however, and is going after the likes of Acer and Asus for licensing fees if the companies decide to offer Android and Chrome OS options in tablet PCs and netbooks. According to the Register, this is $10-$15 that Microsoft wants for each device sold.
Microsoft's claim is that it owns patents related to e-mail, multimedia and other functions.
Acer and Asus aren't the only Taiwanese companies pressured by Microsoft to pay up. HTC has already signed to license the technologies from Microsoft.