Across the USA, there has been interest among the State Departments of Transportation (DOTs) to investigate alternative technologies to estimate travel time such as the use of cell phones as travel probes. This project "Travel Time Estimation using Cell Phones (TTECP) for Highways and Roadways" was initiated by the Florida Department of Transportation (FDOT) at Florida International University (FIU) in September 2004. This report summarizes our studies and investigations regarding the maturity of cell phone technologies for application as real-time traffic probes for travel time estimations along the highways and roadways. Also, the reliability, accuracy, and reproducibility of the travel speed and travel time computations based upon the cell phones as travel probes have been investigated and compared with other methods such as the 511-based operations and Global Positioning System (GPS) - based measurements. The FIU TTECP team has found by virtue of their investigations that the cell phone technology is viable and mature under the normal conditions of free traffic flow, for the travel time estimations. However, the team has also found that the cell phone technology is not accurate in congested traffic conditions, where the data is more important than in the free-flow traffic conditions, and the accuracy decreases rapidly as the congestion increases. The details are provided in the executive summary and the conclusion sections. Additional issues remain such as: (1) privacy of the cell phone users whose phone transmissions are being probed by the cell companies for location data, (2) irregular and transient cell data for travel time and speed computations, especially during congested traffic and severe weather conditions, (3) limited capabilities of the travel time providers to follow changes by the cell companies in their data formats and structures, and (4) incompatibility of data when switching from one travel time provider to another (with different affiliations with the cell phone companies). These issues should be addressed and viable solutions should be found.