A Google search is always a good idea.
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"A dedicated phone connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24 individual channels, each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1 access.
T-1 lines are a popular leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet backbone itself consists of faster T-3 connections.
T-1 lines are sometimes referred to as DS1 lines."
From
http://www.webopedia.com/TERM/T/T_1_carrier.html
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And this page looks quite good for information on all sorts of connections:
http://www.t1-t3-dsl-line.com/
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In theory the different connection types referred to in Limewire refer to speeds, from slow (modem) to very fast (T3). You will, by your own experience decide if this is in fact true
