Large-scale wireless sensor network (WSN) deployment is a major challenge for Internet of Things (IoT) to connect physical world through sensors or tags at the scale of billions of objects. Today's WSNs normally use dedicated gateways to bridge sensors and IP networks. The installation and maintenance of such a WSN infrastructure are expensive and non-scalable. As the number of smart phone users grows exponentially every year, a powerful mobile computing platform could be used as an alternative WSN infrastructure, which is ubiquitous and scalable. This paper studies the major challenges of using mobile phones as spontaneous gateways of WSNs in IoT systems. The challenges include (1) matching the throughput of mobile phone gateways and sensor data rate at hotspot locations, (2) securing sensor data access and (3) providing accounting records of gateway the service offered by mobile phones. In this paper, we show that using a name-based future Internet architecture (FIA), such as Mobility First, these challenges can be overcome effectively though its native networking layer functions. A proof-of-concept prototype system demonstrates the feasibility of proposed solution. The system delivers a temperature sensor data from an Android phone directly to multiple applications via in-network multicast over an Mobility First network test bed.