Best way to get a local phone number (Bangkok)

Hi, all

I need advice from you Expats in Thailand what the best way to get a local mobile phone number is.

I am arriving Bangkok in the afternoon of this Sunday. I will bring a smart phone that I used to use in China. The SIM card is changable. Can I just buy a local sim card and insert it into my phone to start using it? If that is the case, what kind of sim card would be suitable for me? I would like to receive calls from both local and abroad free.

If I want to have this done on the day I arrive, where is the best place that I should go? Should I just do this in the airport? Do I need my identity like the passport to register for a number?

Warn me anything that I have to pay attention.
Many thanks.
Youngji