Android VOIP application - problems establishing a voice(RTP) connection

I have an Android VOIP application which has problems establishing a voice(RTP) connection. The application actually has two voice connection implementations: a custom one based on Sipdroid and an implementation made using built-in Android RTP API ([login to view URL]). And you only need to fix ONE of these. The first(Sipdroid based) implementation doesn't work reliably - from some reason it occasionally fails to transfer voice (RTP) data between the caller and callee. Plus it rarely succeeds in establishing a connection between the caller and calle if one of them is using a Samsung phone. It appears that UDP hole punching doesn't work very well on Samsung phones. The second ([login to view URL]) implementation works almost perfectly. Its sole problem is that it has a terrible 2 - 4 seconds latency. I.e. it takes between 2 and 4 seconds for caller to hear what the calle said and vice versa. So, long story short I need someone familiar with RTP protocol, Android networking and perhaps VOIP in general to either fix the current code or create a new RTP layer from scratch. If you have ever created a VOIP Android app that uses RTP protocol to transfer voice data you should be capable to fix this. Note that your job on this project is just to take care of RTP related code, everything else is in place and working. If you don't have experience with this kind of applications don't bother bidding.