I am with AIS and pay more than 3000 bhat for 1 year unlimited internet on my phone registered to my name. The phone plan is pretty paid with internet package on top called mao mao I think, cannot access AIS to verify.
I do not think there is any relief from import tax unless your nation returning from overseas. Best thing is contact a moving company and get clarification from them. Imported goods from Australia and the duty was not that much compared to the value of goods.
Peter best you look at the thai imigration website got all the information there you need. If not yet married best to get single entry non O and then extend as required either marriage less money in bank but need proof of marriage and residence.