Most people prefer a Face to Face conversation rather a message.  Connection with another person or several people is enhanced by being able to "see them" and there are several Apps available that can replace / supplement phone (voice), text and email contact.  This contact may be with other members but also contact with family and other friends is equally important for us as well as those we are contacting.
Many Apps rely on either membership (Facebook Messenger), Google Hangouts, WhatsApp etc and connecting can rely on the type of device that each of you have.  Generally we know whether our family or close friends use Facebook and we may be aware of the type of phone they have (iOS or Android) but we may not be aware of what other Rotarians use to connect
FACETIME  may be used to connect via voice or video with one or up to 32 friends.  It is especially useful when compared to Zoom for small, informal groups especially family members
MESSAGES  Most will have sent or received messages via this App which comes with iOS devices.  It can also be used on both an iPHONE (sends message via SMS or internet) and on the IPAD (message ONLY by  internet to other iPhone or iPAD owners.
Group Texts
There are a number of Apps that will allow you to connect across both iOS and Android smartphones
WHATSAPP  is an App works on both iOS (Apple) and Android devices BUT needs to be downloaded from the App Store or Google Play.  This App does require that you have an account BUT has a good reputation as an App
  Messenger  Facebook Users and Facebook "friends"  It is possible to create Groups and hold Group Chats by text, voice or video
  Hangouts requires a Google Account.  All GMail users have a google account but it is possible to use a different email provider and have an email account. Voice, Video, Text and Group chats are available
  Skype is the original video connection is still valuable but does require an account (free)
FROM IPHONE I can only advise how to tell from an Iphone.  Open contacts (or enter details as a new contact)  
If the contact has Facetime (they have an iphone) the the options for using Facetime will be shown
as in this example.     
WHATSAPP  If you have WhatsApp installed and open Contacts from WhatsApp it will be clear who has the App on their phone (whether iPhone or Android