Our recommendation for smartphone-optimized sites is to use responsive web design, which means you have one site to serve all devices. If your website uses responsive web design as recommended, be sure to test your website on a variety of tablets to make sure it serves them well too. Remember, just like for smartphones, there are a variety of device sizes and screen resolutions to test.
Another common configuration is to have separate sites for desktops and smartphones, and to redirect users to the relevant version. If you use this configuration, be careful not to inadvertently redirect tablet users to the smartphone-optimized site too.
The post added some information on user agents:
For Android-based devices, it’s easy to distinguish between smartphones and tablets using the user-agent string supplied by browsers: Although both Android smartphones and tablets will include the word “Android” in the user-agent string, only the user-agent of smartphones will include the word “Mobile”.
In summary, any Android device that does not have the word “Mobile” in the user-agent is a tablet (or other large screen) device that is best served the desktop site.