NetTools by Terminal Software works with iPhones, iPads and iPod Touch devices running iOS 4.3 and up. It has three network tools for DNS lookup, ping and traceroute. The ping tool lets you measure latency, and traceroute shows which servers and routers traffic travels through to help you find and resolve bottlenecks. NetTools is also the first traceroute application for iPhones that can do reverse-DNS lookup. The app costs $3.99.