In my Xperia Z review I called the PlayStation Mobile lineup an embarrassment. It looks like Sony might be ready to do something about it, as they are currently waiving the £65 fee to become a registered PSM developer.
As detailed on the PlayStation blog, becoming a PlayStation Mobile publisher will allow you to publish your games (developed in C#) to PlayStation Vita as well as PlayStation-certified mobile devices device, free of charge.
Everything you need to know about developing for PSM can be found on the PSM Dev Portal. Enough to tempt developers over or is the sticking point something else? Time will tell!