How to understand this text message from China Mobile? About mobile phone traffic.

You currently have 2 traffic packages, one is 150M that you ordered for 20 yuan, and the other is 150M for 0 yuan and is limited to use within the province (this should be a preferential experience provided by the operator, etc.). According to the operator's default billing method, when there are multiple services of the same type, the one with the cheapest tariff will be used first. If you use it in Guangdong, you will give priority to using the free 150M, and only use your own 20 yuan package when it is used up. If you go out of province, you will use your own 20 yuan package.