Can I use iMessage or RCS (Rich Communications Service) without a data plan?
To use iMessage or RCS you need an internet connection (with a Shaw Mobile data plan or WiFi).
Without a data plan or WiFi connection, you will get an error message while sending. To prevent error messages, you can either:
Turn off your data connection.
Disable iMessage or RCS in settings.
Group Messaging with MMS is a great alternative to iMessage or RCS, and doesn't require a subscription to a data plan (though you will need to make sure that your data connection is enabled for it to work).