Can Xiaomi mobile phone watch only send messages by voice?

Not exactly. You can also send text messages.

The method of sending text messages on this mobile phone watch is the same as that on the mobile phone. After opening WeChat, click on the other party's micro-signal, then input the information content with handwriting input method, and then click Send.

Xiaomi mobile phone watch, if you want to send text messages, you must install a sim card in the watch, that is, a mobile phone card. Without this card, you can't make phone calls and send text messages.