ILEC GUI is the internal terminology for the series of (usually) web based utilities that allow CLECs (CLEC refers to competitive carriers such as Sprint, MCI, ATT or other smaller carriers who don't have physical on premise presence) access to the local phone network. These allows CLECs to maintain their own customers by allowing them to establish, change, move or disconnect telephone service. They also allow them to add/remove features via USOC codes and to schedule repairs. There are 5 major GUI's that most CLECs will utilize:

Verizon LSI

Covers Maine, Vermont, New Hampshire, Massachusetts, Rhode Island, New York, New Jersey, Pennsylvania, Maryland, West Virginia, Virginia, Delaware and Washington DC.

Bellsouth LENS

Covers North Carolina, South Carolina, Georgia, Florida, Alabama, Tennessee, Kentucky, Mississippi and Louisiana.

QWEST IMA

Covers Minnesota, Iowa, North Dakota, South Dakota, Nebraska, Montana, Wyoming, Colorado, Arizona, New Mexico, Utah, Idaho, Washington and Oregon.

SBC Toolbar

Covers Connecticut, Ohio, Indiana, Illinois, Michigan, Wisconsin, Missouri, Arkansas, Texas, Kansas, Oklahoma, California and Nevada

GTE WISE (Verizon)

GTE has a presence in nearly every state in the union, but most notably in California, Oregon, Washington, Indiana and Ohio. Verizon is planning to merge this GUI into LSI as WISE is rather cumbersome to use.