According to this, sony requires ISBN numbers to publish:
Sony requirements from their website:
"If you are an independent author or a publisher with only a handful of titles, please sign up with one of the following self-publishing companies to make your titles available at Reader Store."
http://ebookstore.sony.com/publishers/
Smashword instructions from their website:
"Smashwords retailers such as Apple and Sony will not accept your Smashwords book unless you have a unique e-ISBN."
http://www.smashwords.com/dashboard/ISBNManager