These low-end models are designed to be released in emerging markets. For example, the BlackBerry Z3 will launch first in Indonesia which is why it originally was codenamed the BlackBerry Jakarta.
If you are a BlackBerry developer, you can decide to opt out of the automatic availability of your work for the Z3. If you do opt out, you can add support for the phone at any time. Developers are receiving emails from BlackBerry that contain a link to a website where they can declare their intention to opt in or opt out for the BlackBerry Z3. The deadline to respond is March 14th at 5PM EST.
Both phones feature a 5 inch screen, although the resolution on the BlackBerry Z30 (720 x 1280) tops the expected 540 x 960 resolution on the BlackBerry Z3.