If Tello supports WiFi calling, the iPhone 11 supports IMS. Using the data of the local esim, you can use the Tello sim for wifi calls and messaging. iMessage will work in wifi mode.

My family has used IMS to avoid international roaming charges for several years. We have made calls to each other while traveling without incurring roaming charges for the calls. A few Android models support IMS. All iPhones since the XR support IMS