I have a postgradaute degree in Wireless Routing Protocols and have been working on ns-2 for the last eight years. I have successfully implemented several routing protocols and metrics in ns-2. I am quite comfortable modifying the source code of routing protocols and MAC layer solutions in ns-2.
MANET routing protocols such as OLSR and AODV are my speciality. In fact, I have implemented several routing metrics such as ETX, ETT etc in AODV. Moreover, I have also implemented several cross-layer solutions (Network interaction with MAC) for these protocols. Similarly, for OLSR, I have worked on several features, such as optimizing the MPR selection and minimizing the TC message overhead by using intelligent techniques.
I haven't particularly used VoIP streams in ns-2, but a little readup has shown me that it shouldn't be too hard to handle.
Apart from implmentation in the source code, I have also develoepd several scripts for carrying out the performance evaluation such as throughput, packet loss, delay, routing overhead etc.
I think I can handle your project quite well. However, more details would obviously be required about the project before finalizing the bid. At the moment, I am assuming that it would be some sort of performance comparison of AODV and OLSR for VoIP traffic in MANET scenarios.