http://3bb.co.th/promotion/en/6mb.php

does this require a one year contract or some other catch ?

Is it correct that the below are all free? in Pattaya if that matters

(1) Registration fee of 100 THB (2) Installation fee of 3,585 THB (3) Protector box fee 100 THB (4) Internal wiring fee of 320 THB

I paid a total of 731.25 for the 6Mb connection in Bangkok; I think it includes a 100 Baht as deposit for the router

Most internet pacakage promotions by Thai ISP nowdays provide basically "free" hookup. The modem/router is where you may incur a small charge although several promotions still provide the router/modem free. A 12 month contract is pretty much standard operating procedure.

what are the rules if you have to break the contract?

what are the rules if you have to break the contract?

Normally you have to pay "what was given free", like the four things highlighted in red in your original post. But sometimes you can get away with giving back any free modem/equipmnet provided and paying a 1000 baht penalty (assuming they didn't have to string a new line to you...then you are probably on the hook for the new line installation charge)--but it varies from promotion to promotion/company to company.