Can I bring any smart phone to Thailand as long as it has a card slot and can be unlocked.Or do you think better to sign up with company and use their phones like we do over here.If I bring a pad over then I imagine I have to pay a server for wifi.

In Thailand the carriers only sell a few high end handsets. All phones come unlocked and there are very few incentives for buying from the carriers as in other countries. So if you have a compatible handset (quad band GSM will do just fine) make sure you get it unlocked and bring it with you. Also if you don't have a work permit the only company that will let you have a postpaid account is DTAC if you have a valid foreign credit as a guarantee for the first three month's service (they only bill the credit card if you don't pay your bill during the first three months of service). Otherwise you can just go to any phone shop, 7-11, etc. and buy a prepaid sim card.