If you are having troubles using iMessage on your iPhone or iPad with a AOW Data SIM card, try switching from using your SIMs as the identifier to your Apple ID (email address) while using iMessage.
To use iMessage with your Apple ID, navigate to Settings > Messages > Send & Receive and tap Use your Apple ID for iMessage. You may need to delete any existing iMessage conversations and then restart the app.
Note that iMessage requires a data connection, so you will need an active plan to send and receive iMessages.
Please note: You will only be able to send iMessage to other iMessage users. If you attempt to send a message to a non iMessage user, the message will not go through as regular SMS text messaging is not included in AOW plans.