IM: Phone number required

• Discord: not required

• WhatsApp required
• Signal: required
• Telegram: required

• https://en.wikipedia.org/wiki/Comparison_of_cross-platform_instant_messaging_clients

Related

• Multi account
• eSIM

See also

• IM, Messenger, Slack, Mattermost, RocketChat, Gitter, Discord, Microsoft Teams, Skype, Amazon Chime, Zoom, Google Chat, AWS Chatbot, LiveChat, APNs, Arattai, Zulip, Chanty, Fleep, Spaces, Zoho Connect, QQ, WhatsApp, Cliq, iMessage