Unless you are taking the route of roaming charges, you are going to want a SIM card. Thankfully, data is crazy cheap here! We’re talking less the $10 USD for 10 GBs.
Any of the the street vendors you see selling electronics up and down Batu Bolong will be able to hook you up with those.
If you would like a local number to make Go Jek orders or any number of other things you can do with a local phone number you either need to have a local lend you their ID for registration or you’ll want to make a trip to the cell phone networks HQ on Sunset road. I’ll be about 30 minutes by bike, so leave early.
Otherwise, just connect to the WiFi where ever you happen to be and chat with people over WhatsApp. This whole island communicate through this. You will actually find that many business use WA over an regular phone line.