How to send a message to a mobile phone with imessage?

In the case that the other party has already opened the iMessage service, Apple does not seem to provide the option of how to send ordinary SMS. In fact, this function is hidden deeply. The solution is actually very simple. Open the information program, click the compose button in the upper right corner, select the friends who have opened the iMessage service, and enter the information you want to send. If you see that the send button is blue, it means that your friend has opened the iMessage service, and the information you send will be sent through iMessage without charging for SMS or MMS. If you see that the send button is green, it means that the other party has not opened the iMessage server, and the information you send will be sent as an ordinary SMS, and the tariff will be charged normally. So, how can you send ordinary text messages when your friends have opened iMessage? After sending the information you want to send, press and hold the sent information, and a selection box will pop up. You can choose to send it as ordinary information. Thank you for your adoption.