What do GSM priority and GPRS priority mean in SMS settings?

Set communication protocol: GPRS: general packet radio service technology, GSM: GSM is the protocol of mobile Internet access. After SMS is set to GSM, the information will be transmitted to the server according to the communication protocol, and the tariff will be subject to local standards. Set to GPRS, SMS is sent in the form of network packet, which can be regarded as traffic, that is, traffic fee. Therefore, the communication of SMS is GSM channel, and MMS is MMS, not SMS, so GPRS must be taken.