Today, almost every phone has dual SIM slots. the easiest ways to transfer contacts from one phone to another is following the steps described below:
a. Select all the contacts of the Existing phone and copy them in SIM.
b. Insert this SIM into the new phone to which you want to transfer.
c. Select the contacts again and Copy them into the new phone.
a. Go to the contacts tab.
b. On the top right corner, there will be a line of three vertical dots indicating menu options.
c. In the list of options, select "share"
d. On the top left, there will be one box or circle to select "all". Tick that.
e. Again go back to the menu and click on share.
f. This time you will several options of sharing, but the best is to choose WhatsApp, since it will need them anyway.
g. Now on WiFi, open WhatsApp and go to contacts.
h. On the settings, select contact again.
i. There select, Manage contacts.
j. From there select import/export option, and select the option that suits you best.
After selecting all the contacts from your existing phone you can select share option the same way, and instead of WhatsApp, you can select any other app like gmail, or Messaging to import the contacts and later download them on your new phone.