The t1 internet access has been around for over 40 years but never have there been so many "flavors" available. The number of providers has jumped since deregulation in 1996 from a few dozen to several thousand. As the telecom shakedown that began in 2001 continues many of these comapnies are trying to stay afloat by capturing as many customers as possible with inexpensive products they claim to be T1. Don't be fooled!
Many of the desperate companies are putting together inferior products they claim are T1 products. Be leary of products with the funny titles like "burstable" and "reach". These products are oversubscribed much like a DSL product. This means the provider put's a singled T1 connnection in a CO (Central Office) and sells T1 connections to 3 or 4 customers hoping they don't all use the service at the same time. True T1 access means dedicated access to the internet and you always have access to 1.54Mbps.
Make sure your T1 product is a "clearchannel" product and is not shared with other users. Also be sure you have an SLA or Service Level Agreement from your provider. A SLA will specify the access you will receive and the penaly the service provider will pay if they do not provide such service. If you need help establishing the proper SLA seek the help of a professional if you don't have one in house. It's much better to pay a small fee up front than to enter a long term contract with an inferior carrier. You can also get professional assistance free of charge by simply contacting one fo the many T1 brokers on the internet.