I was curious if anyone had any experience or knowledge of usability tests on button sizes on mobile. My company is currently using a button that spans the entire length of the mobile screen, but I wanted to know if having a more tradition button that exposes all 4 sides was more effective.
Are we talking native or web here? If native, all the OS vendors provide best practice specifications on touch targets as well as their implementation. Search for Windows / Android / iOS design guidelines. Otherwise minimal target averages at around 9mm with 2mm padding - see: http://www.lukew.com/ff/entry.asp?1085 (some good links in there)
Since you titled the question as CTA buttons, I am assuming this is the main action you want the user to take (not part of navigation, etc.) and hence it being displayed at block level (full width) is recommended and makes it easier to interact with. Only concern is recognition. When you say "entire length", do you mean literally from edge to edge of screen? As you stated all four sides should have some distinguishable padding (in the background color) as to enhance interaction recognition.