Hereof, can a deactivated phone use WiFi?
Yes. Your phone will still receive a data while connected to WiFi, similar to how a tablet works. Streaming services such as Pandora and Spotify would connect using WiFi but not over the cellular network.
Secondly, can I use my old smartphone on WiFi? Turning an old Android smartphone to a dedicated Wi-Fi device only is quite simple to do. As a matter of fact, all you have to do is turn off all cellular network and features and that's it. As a dedicated Wi-Fi device, not only you preserve the battery of your brand new phone, you also prolong its general lifespan.
Also asked, can I still use my phone without service?
The short answer, yes. Your Android smartphone will totally work without a SIM card. In fact, you can do almost everything you can do with it right now, without paying a carrier anything or using a SIM card. All you need is Wi-Fi (internet access), a few different apps, and a device to use.
Can I use WiFi on my phone without service?
Rest assured that your phone will operate just fine without active service from a carrier, leaving it as a Wifi-only device. Whether you're buying to use the phone on Wifi permanently or just for a short period of time — perhaps while you're traveling abroad — you won't find many issues.