Not that difficult, mate. First day tell them to take out their cell phones, than ask: Does anyone want to sell your phone today? They'll be some yes' and some no's.
Well, I want to sell mine. And you want to sell yours as well. First I'll sell mine ... what should I do? You'll get "let me see it" or something close. You say, no. I want to show it to more public than you OR this class. I want to make an adver. Take out your phone, (if you have one) draw it on the board. Then ask about a phone's features. They'll say: camera, video, bluetooth, etc. You say, no, mine has none of that, does yours? (to the Ss) So take out your phone and do what I have done - make a flier and made your presentation to the class ... I'll go first. Slowly finish your over-sized flier listing everything you can think of, features, the phones age, the ad-ons, price, your phone #, etc. Then sell your phone to the class, first. Then ask them to do the same.
All Thais have mobile phones, if they don't they're not Thai This will break the ice over talking cause they have something in their hand they know a lot about, and get the chance to show it off. Thais are proud of their phones. If a S pulls out an old beater make fun of it with him/her. Say the word, CHOY (out of fashion) in a laughing way. They'll like that, it's the Thai way. Whatever you do you must make your class fun. Ss must look forward to going there. It's all up to you, bro.
PS get there early on turn on the AC. 40!!!