Cellular operators have been offloading data traffic from their licensed bands to unlicensed bands through a large number of WiFi hotspots over the past years. Although this approach improves the cellular network capacity to some extent, it falls short of getting significant throughput gains. In this paper, it is argued that femtocells, covering a short range, can be a perfect platform to jointly exploit the merits of both licensed and unlicensed frequency bands. In particular, a framework is proposed for a femtocell to simultaneously access both licensed and unlicensed bands. The performance of coexisting femtocell and WiFi networks operating over a fully-utilized unlicensed band are analytically modeled and are verified via simulations. Impact of femtocell channel access parameters on the performance of WiFi and cellular networks is also investigated, shedding light on how a femtocell can best adjust its channel access parameters to coexist with incumbent unlicensed spectrum users like WiFi networks.