Wow, that's really small. Actually it's what phones used to be before 2007.
I got one off the kickstarter, and it's a neat little gadget. It hasn't fully replaced my main smartphone, but it's great for outdoors activities, or if I'm wearing an outfit without big pockets and don't want to carry a bag.
Did get another SIM or move the one from your phone into the Atom?
I swap my SIM when I want to use it, but it would be less hassle to get a separate one.
But then, how do people contact you? Anything tied to your phone number wouldn't work. Perhaps only Telegram, Skype, Messenger work cross device. Phone calls and WhatsApp don't.
For phone calls, good old call redirect is still a thing :P
No idea about whatsapp though.
If I'm out cycling or paddling, I probably don't want to be all that reachable, anyway.
I have the original Jelly phone, and it's actually smaller than Nokia phones I used in pre-smartphone days.