Here's the link to the manual of Tamagotchi ON circulating on the Net.
These are some pictures of the Tamagotchi ON
There is a screw instead of a button due to security regulations for toys in the US.
Find out more pictures here.
Internal pictures of Tamagotchi ON :
The speaker is different from Tamagotchi Meets.
Check out here for more internal pictures.
All the information above is found by Mr. Blinky