Yes, you can use iMessage with a Textr eSIM cellular data plans. iMessage is a messaging service provided by Apple that allows you to send and receive text messages, photos, and other types of media over an internet connection. To use iMessage, you need a device running iOS or macOS and an active internet connection, either through Wi-Fi or cellular data.

If you have a cellular data plan, you can use iMessage even when you're not connected to Wi-Fi. Your iPhone will automatically use your cellular data plan to send and receive iMessages. The amount of data that iMessage uses can vary depending on the size and number of messages you send and receive, but it's generally a relatively small amount.

Note that if you have a limited data plan, using iMessage (or any other internet-based service) can consume some of your data allowance, so it's a good idea to keep an eye on your usage and monitor your data usage regularly.