Can I use Canon TS6420 to print from BOTH my computer AND smart phone? Or is it just one or other??

[shadowsports]

Greetings,

You can use both, or any device connected to the same network.  The printer also supports bluetooth.

Note, this might not work reliably if you are using a USB connection directly to a single device.  

Standard interfaces on this device:

Hi-Speed USB
Wireless PictBridge
Wi-Fi® (802.11b/g/n wireless networking, 2.4 GHz)
Bluetooth 4.0 LE (Low Energy)