Can I still text on my iPad when I take service off my phone?

No, but you can continue to send iMessages to other Apple users. Texting requires a iPhone connection.

An iPad without a cellular modem or active cellular plan can still text using WiFi but with restrictions if you are using the Messages app. You would need to use a third party texting app like WhatsApp.

From ChatGPT:

Yes, an iPad with only WiFi can still send text messages, but with limitations:

1. iMessage – If you’re messaging another Apple device (iPhone, iPad, Mac) with iMessage enabled, you can send texts over WiFi. These messages appear in blue bubbles.
2. Third-Party Apps – You can use apps like WhatsApp, Facebook Messenger, Telegram, or Google Voice to send messages over WiFi.
3. SMS/MMS (Green Bubbles) – No Direct Support – Standard SMS/MMS messages (used to text non-Apple devices) require a cellular connection. However, if you have an iPhone, you can enable Text Message Forwardingin your iPhone’s settings to relay SMS texts to your iPad over WiFi.