Why does my iphone4 always have the option "Cellular data is off, cellular data or WLAN is enabled to access data" when sending text messages?

This has little to do with texting. The reason for this is the following：

1. Your mobile phone may be running programs that need to connect to the network in the background. It happens that your nest peak data is closed, so you will be prompted to open the data, which is what you call the phenomenon.

2. If your IPHONE turns on push, notification or automatic software update, the above prompt will also appear.

Solution: Go to Settings-General-Network-Enable Nested Peak Data. Or close the background program and push the notification, as long as you don't run the program that needs the network.

I hope my answer can help you.