T3 or DS3
This is a 43 Mbs connection. The local loop to the service provider is installed for 43 Mbs, however your access port is normally setup for a slower rate. The local loop connection consists of 672 individual channels. Each of those channels supports 64Kbps each. This connection is quite expensive and it can be installed to only use some of the 672 channels to lower the cost. A T3 or DS3 has the same capacity of 28 T1s.
You should start with maybe 9Mbs or higher service. If you only ask for say 6Mbs you may find that bonded T1's are cheaper. The advantage of the T3 over a T1 is that it has greater flexibility to expand up to that maximum of 43 Mbs.
When you get a price on this T3 or DS3 service you should also ask if you pay for the local loop or is it included in the price from your bandwidth service provider. A POTs line or (plain old telephone) line will not carry this signal.