I don't see any reason why it cannot get any PR while being in sandbox. Some of my domains with nothing on them have PR (just some old links, there's not site/content on these domains at the moment).
Most of our sites go on-line quickly. Therefore get indexed quickly. If, the site gets two indexes before a PR update, then it gets PR. One - no PR. But we have solid navigation and use a Sitemap via WMT. Most will also jump 1 PR after the next PR update. All this while in the first 6 to 8 months (Sand box), but most ranking suck.
I have seen some indexed domains with a PR although they are not functionally active websites,so i guess its possible