This paper presents experimental results of a heterogeneous sensor network architecture, which is a combination of a wireless sensor network and a personal area network. The proposed architecture uses the IEEE 802.15.4 standard to transmit sensor data to a sensor node which in turn forwards the data using TCP/IP to a database on the Internet via a Bluetooth-equipped mobile phone and the mobile telephone access network. The performance of the entire communication chain is evaluated. First, a 3G network's performance is evaluated by measuring its round trip time for packet transmission. Second, the real-world end-to-end delay between a sensor node and a database server on the Internet is measured using two different experimental set-ups: single-hop transmission and two hops transmission. Finally, the proposed architecture's scalability is estimated in a Matlab simulation using the results of the experiments as a base. The results show that the proposed architecture is applicable for small-scale sensor networks used by highly mobile users.