How does China Unicom use SMS 2g to upgrade 3g?

If you are referring to the Unicom package you are using, the 2G users of Guangdong Unicom can change your 2G package into a 3G post-paid package in their own business hall due to the different changes in different provinces. If you need to upgrade to 3G prepaid package, if you need to upgrade to dual 4G traffic king (formerly: Wo traffic king), just send a text message. Prepaid users can send short message "ZTC+3252" to 100655. Send the short message "ZTC+325 1" to 100 10 to switch to 25 yuan dual 4G traffic king package, which needs to be sent before 25th of each month, excluding 25th.