Tourbuzz uses a 3rd-party service called Voiceover Toolbox to create voiceovers. These voiceovers are created from a bank of professionally recorded phrases.
Occasionally customers will request a custom voiceover for their tour, which we also support. Voiceovers can be added to each individual slide or as one long clip for the entire tour. Custom voiceovers are typically around $100 for a 2-3 minute project.
We recommend Jessica Binstock for custom voiceovers: http://www.jessicabinstock.com/.