How to use iMessage independently with two iPhones using one AppleID

If you cannot use iMessage, you can turn on iMessage in Settings → Messages, and you can use your mobile phone number Apple ID to receive it. When sending text messages, if the contact you choose has activated iMessage, your iPhone will automatically use iMessage send. There is no SMS fee for sending iMessages, and you need to use an active wireless network or cellular data to send and receive.