This writeup is quite short by design, but provides a good sense of the opportunity, especially for service providers looking to offer VoIP and/or UC to their SMB customers. Lots to consider, and if this speaks to your current situation, I encourage you to give it a read.
Today, Metaswitch formally announced the paper on their blog page, and you can also access a download link from their Resources page, which also provides other reports, papers, etc. worth checking out. Would love to hear your thoughts, and by all means, please share as you see fit.