Most service providers have different price options based on connect time. Some common options are rates based on hours per month, ie. Some service providers charge a fee to sign you up to their service in the beginning. This is the fee they charge for you to establish an account with them. If you are dialing a number that is not considered a local phone call, you will be faced with paying not only your service provider's monthly fee but long distance charges on your telephone bill as well.
Some providers offer limited free trials to potential customers so it pays to ask.
Others can be much more limited. Think about when you will be using their service the most. Many service providers these days will give you free web browser software and communications software such as Winsock when you sign up. Most service providers will automatically charge your credit card account, Some will bill you if request. Sometimes there is a discount if you are able to pay for a specified period of time in advance, such as a year, for using the provider's service.