When looking for an internet service provider, you need to consider
Business Broadband plans may entail a service guarantee, that ensures that the network has 99.9% uptime and you are credited for downtimes under the terms of the service guarantee. All internal traffic within your network may also be FREE. Therefore, you will save money on ISDN and data traffic between company sites and free I.T.staff within the company to engage in other important activities rather than worry about the status of the network. There are business broadband providers that specialize in these kind of services and will assist you to integrate your intranet to compliment business broadband arrangements and deliver organisational benefits and improved efficiency.
If you do not need a specialized business broadband connection, then
It is better to overestimate the amount of data traffic that you would expect to use, especially if the excess data charges are substancially more than you would pay on a plan. Some broadband providers chose to reduce the speed of connection rather than charge for excess data but others charge an exhorbitant amount for excess data and a bill in the thousands of dollars could await you if you are not careful managing your usage. And even if you are careful in managing your usage, data can be incorrectly measured. eg. a 20K file is metered for 1000 times more.
It is quite common for the Telecommunications Ombudsman to receive complaints about overcharging of data. And our own personal experience is that often, companies will apply you a small credit when you complain, full knowing that their systems to measure data are buggy and inaccurate. Avoiding any plan with excess data charges could save you thousands if not tens of thousands of dollars and legal hassles
It is very difficult to prove that you did not use data or that you were overcharged for data that was used. You really need to trust your ISP.