As soon as I received the text message, my cell phone lost signal.

This problem is probably because the high-definition call is not opened, and the internet and the call conflict cannot be carried out at the same time.

Now suppose you have an ordinary 4G+ mobile phone and 4G card, find "Wireless and Network" in the settings, and turn on the "VoLTE HD Call" function of the mobile phone SIM card in "Mobile Network". After success, a high-definition icon will be displayed on the SIM card where the signal icon is displayed.