Based on Agents strings on this site:
http://www.webapps-online.com/online-tools/user-agent-strings
This results came up:
First:
All Tablet Devices have:
1. Tablet
2. iPad
Second:
All Phone Devices have:
1. Mobile
2. Phone
Third:
Tablet and Phone Devices have:
1. Android
If you can detect level by level, I thing the result is 90 percent true. Like SharePoint Device Channels.