Didn't the other party open imssage to recover the phone bill?

There is no phone bill, only traffic consumption.

Imessage actually sends information through the network, which means it uses traffic instead of SMS. To realize imessage between two Apple products, both devices must be connected to the network, or the two devices are very close and connected by wireless means such as Bluetooth. If you can't get online, you can't use imessage for free, and you can't successfully send messages with imessage. The information mode will be displayed in blue. Send messages by ordinary SMS, which is green and environmentally friendly. So there is no charge for imessage.

Imessage is an instant messaging software launched by Apple, which can send short messages, videos and so on. It has high security. Imessage is different from SMS/MMS service of operators. Users only need the data support of WiFi or cellular data network to complete communication. You can send text messages, photos and videos to other mobile phones through the cellular network. You can even ask Siri to text you. Just say "Tell Xiaoli I'm on my way" and Siri will help you write and send messages.