In this latest dev blog on the official Star Wars: The Old Republic website, we're given a peek into the process behind the massive undertaking that is committing to full voice-over in The Old Republic.
The blog gives us some backstory to the concept of including full voice over in the game by giving us a peek at what is essentially a phone log discussing the idea. Of course, just as most of us thought when we heard the idea, the guys behind the game thought it was just as crazy.
Nevertheless, both BioWare and LucasArts are committed to this and the general process involves BioWare writing out the scripts and the guys at LucasArts doing the recording.
The game is described as having enough voice-over to span ten KOTOR's. Voicework is recorded in at least five cities, they've worked with hundreds of actors so far, and there is over 40+ novels of content. They say the hardest part of it all is maintaining consistency. For example, there are many ways to pronounce "Thul" or "Holo" projector, and so they have maintained an audio pronunciation guide to help with that.
For much more information, dig into the full dev blog here.