walkie talkie type apps

I am looking for an accessible, hopefully free, and reliable app for chatting among a group. Does anyone have suggestions? I personally have used whatsapp, zello, allo, and voxer. Voxer's voice features behave strangely with VO in my experience, IE audio routing through the earpiece, but the realtime messages seem nice. Whatsapp seems very user friendly, but I don't know how delayed messages are. Same with Allo. Zello sounds nice, but I'm not sure how the group part works in there. Any ideas for simple yet user friendly and reliable would be great. Thank you.