Il modo migliore per spostarsi è tramite escursioni organizzate (sia dall'Italia sia direttamente in Thailandia).

Hi, We took Golden triangle day tour which began in Chiang May and finished in Chiang Rai. So, one option is to take a day tour from Chiang Rai. In Soap Ruaki port there are many boats waiting for tourists. You can join group or take a private boat. As I know, Thai people are very honest, so it should be safe to leave the car to the parking lot.

I think you have selected the wrong place for your question. Or Tripadvisor messed it up. This place, the Golden Triangle is in Northern Thailand. There is mobile roaming provided. Local mobile providers are DTAC, AIS or True. The ones you ask about are based on the Maldives and are not available in Thailand. Likely they have roaming contracts with the local providers here. This is a question which needs to be directed to the providers of your sim.