A call tracking system and method that uses a pooling algorithm to manage a pool of telephone numbers that are utilized in advertisements. The pooling algorithm allows adjustments to be made to the pool in order to achieve a desired degree of call tracking accuracy performed by the system. The pooling algorithm may adjust the pool in terms of size, quality, or other metric, and assign phone numbers so as to meet the desired accuracy requirements. While additional numbers in a pool may increase accuracy, fewer numbers result in lower cost, and a balance may be struck based on the requirements of an advertiser. When a phone number is to be provided for an advertising campaign, the phone number may be selected from the pool randomly, in round-robin fashion, or according to criteria related to expected accuracy.