Vivo mobile phone has no card, why can't I send text messages?

You can't send and receive short messages without a sim card. However, if you use an iphone, when the iphone is connected to a wireless network, it can send short messages without a sim card. This short message is called imessage, and its color is blue, which is different from the color of ordinary mobile signal network (green). If you use an iphone, just look at whether the message you receive is blue or green. If you use a VIVO phone, you don't know what this is.