We propose a new evaluation approach to evaluate the service scalability of network architectures, that aims to study service scalability of network architectures in current Internet architecture and help evaluate designs of next generation Internet (NGI). The key idea is to measure existing network services using the concept of service utility. While service utility indicates whether service deployed in network can get good achievement which considers the index of user satisfaction in network service usage and network costs. After analyzing different types of services existing in current network, we explain the design rationale behind this evaluation approach and present analysis results of different types of services in different network architectures. The analysis results show that our approach is feasible to evaluate service scalability of network architectures, even if it needs further study to evaluate service scalability of the whole Internet architecture with more powerful cost and utility functions.