Hi, form my opinion, First, you mentioned SMS and GSM, sms don't have a acknowledge for reply, and for this don't have a strong communication, other way, if you evaluated diferent provider technologies? like CDMA or iDEN, this is important becuase the provider let you a good level for tracking, all the fleet depend of a good service provider, means a good signal reception for SQE, RSSI in your country for the type of AVL, it's 50% of all the project, and Second, you have to separate the software of communication Server/avl, database, and finally the rest of packages, web pages, server maps, acces, etc!