Are there any BlueTooth apps that can connect two (or even more) inactive phones to talk with each other as if they're Walkie Talkies?

Isn't the range of Bluetooth too short for something like this?

Pre smart phones there was a Bluetooth chat client for Sony Ericsson phones.

Have you tried Bluetooth Walkie ?

I've not used it myself, but the blurb on the Play store sounds like just what you need.

Bluetooth range is too short and too unreliable for that that work well. A good rule of thumb is if you can't hear the other person, neither can Bluetooth. There are apps that use WiFi or internet ofr this. This app is free for WiFi and you pay if you want to cross internet https://play.google.com/store/apps/details?id=com.slide2talk.android.app

Not a "voice chat", but Briar exist for text chat, and sending images in a one to one conversation. You can also have forums and group chats. If you have like a bunch phones with Briar installed, you can have a mesh network for communications, using Bluetooth. Also works via connecting to the same Wifi network or via the internet through Tor. Think of use cases like protests, and the government shut down the internet and cell towers, with enough protesters intalling Briar, you can still organize "off the grid".

Sounds like a cool idea. I’ve never heard of any apps like that.

If you could get them all on wifi, you could use an app like Threema or Signal to do voice calls.