Does it cost money to send text messages with imessage?

No charge. In fact, IMESSAGE 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. People who send messages by ordinary short messages are green. I hope my answer is helpful to you!