This paper presents the findings of an extensive measurement study on multiple commercial third-generation (3G) networks. We have investigated the performance of those 3G networks in terms of their data throughput, latency, video and voice call handling capacities, and their ability to provide service guarantees to different traffic classes under saturated and lightly loaded network conditions. Our findings point to the diverse nature of the network resources allocation mechanisms and the call admission control policies adopted by different operators. It is also found that the 3G network operators seem to have extensively customized their network configurations in a cell-by-cell manner according to the individual site's local demographics, projected traffic demand, and the target coverage area of the cell. As such, the cell capacity varies widely not only across different operators but also across different measurement sites of the same operator. The results also show that it is p...