Courtesy of:

AC - Authentication Center
Contains cryptographic information that allows the network to determine that a mobile is valid. Usually contained within an HLR.

BS - Base Station
Contains the radio equipment for one or more cells.

GT - Global Title
An SS7 address type based on a telephony number, such as a calling card number, IMSI or MIN.

HLR - Home Location Register
Contains information about a subscription, including the types of services which are to be provided.

IMSI - International Mobile Subscription Identity
This 15 digit number can be used to identify mobile phones to a BS.

IRM - International Roaming MIN
A special type of MIN that identifies a mobile outside the NANP. An IRM always begins with the digit 0 or 1.

MAP - Mobile Application Part
A protocol specifically designed to support roaming.

MC - Message Center
Stores and forwards short messages.

MIN - Mobile Identification Number
A 10 digit number that uniquely identifies an AMPS or CDMA mobile.

MSC - Mobile Switching Center
Connects mobiles to other mobiles or to phones in the telephone network or on other cellular systems.

TLDN - Temporary Local Directory Number
A number that is used to route a call to a roaming mobile, to enable call delivery.