How do I enable MMS messaging to see if a SIM card is compatible with my iPhone 6s Plus

Open Settings ➡️ Messages ➡️ MMS Messaging: Ensure that this switch is set to ON.

If MMS messaging still does not work, then contact your carrier for further information to get this feature activated.

Axel F.

Only enabling MMS on an iPhone is not good enough, get in touch with your carrier and understand their pov on SMS and MMS for the SIM and Data plan that you have

• To send texts to Android users (In a group or Individual) you need an SMS plan enabled by your carrier for the SIM/eSIM that you use on your device. Apple Inc does not provide SMS services. There are no settings on an iPhone for sending SMSs to Android users simply ask your carrier to enable this for the SIM that you use.
• To send images/files to Android users (In a group or Individual) you need MMS enabled by your Carrier for the SIM that you use and then enable it in your Settings. See the Pic below

To be able to use any SIM across the globe you must have "No SIM Restriction" against Network Provider Lock. Please refer to the pic below.