In recent years, with the evolution of new and content-rich Internet services, mobile network operators face the challenging task to guarantee ubiquitous and seamless access to their customers, while minimizing the installation and operating costs of their network. On the other hand, in residential areas most of the network capacity that residential users lease from ISP for Internet access remains unexploited. Mobile network operators can therefore rent the unexploited capacity of residential user access devices (e.g., wireless access points or femtocells) when the traffic demand of their mobile customers exceeds the operator's network capacity. To minimize the leasing costs for the use of the capacity made available by residential users and prevent market manipulation, we formulate the allocation mechanism as a combinatorial reverse auction, which guarantees that all users reveal their real price for the utilization of their wireless access points.