Signal works with dual SIM phones for insecure SMS/MMS. Enable all permissions for Signal under your Android Settings for this to work. Long-press the gray-send icon to choose which SIM card will send an insecure SMS/MMS message. Signal references the names of your SIM card as identified in your Android phone's settings.
To see dual SIM options
- Update your OS to Android 5.1 or later.
- Go to your Android phone > Settings > SIM cards > check the SIM labels.
- Make sure your SIM is enabled and has a mobile plan to send SMS/MMS. You may want to physically swap the SIM cards on your phone.