Hmm, where did you read this?
LSP is probably to do with Link State Protocol, or link state packet. The packets that routers exchange to communicate with other routers on the Internet and establish the best route to send data through. The delay/latency on a VoIP call could be because the Internet is busy at that moment in time (general network latency) and, or because the VoIP server is busy and buffers input/output accordingly. The problem with VoIP is that it uses udp packets which are not as 'intelligent' as tcp packets to control integrity of the data. So, to avoid dropped packets and out of sequence data (which would make voice messages unintelligible) the VoIP voice call applications (e.g. Skype) use their own voice engine buffers to manage the transmission and reception/ordering of packets. Not withstanding the previous comment about network latency/contention, some voice engines seem to be better at managing voice data traffic than others.
Interested to read what the LSP article you mentioned says.
