The recent growth in traffic loads in cellular networks has seen the need for a better use of system resources as its expansion is expensive. In the cellular base station (CBS), the bandwidth availability is limited. Thus, in cellular networks the call admission control greatly influences the system performance because it determines the bandwidth use of the CBSs. The network performance can be evaluated by parameters such as new call blocking probability, handoff call blocking probability and bandwidth utilization. This work proposes a call admission control that carries out the bandwidth borrowing when a call arrives and there is not enough bandwidth. The system makes use of a heuristic mechanism that determines the available bandwidth for the new calls according to some parameter values of the system. The bandwidth borrowing is applied to the cell ongoing calls until the minimum levels for each type are met. The algorithm was applied to the bandwidths and characteristics of a 3G network. It was also applied to a GSM/GPRS (global system for mobile communications/ general packet radio service). The results show improvements in all parameters.