For domains with less competitive keywords, sandbox should not be a problem. I do not know about subdomain stuff, but I feel if you take the following steps you can come out of the sandbox quicky
- Add as many incoming links as possible with appropriate anchor text to overcome the effect of 'new links dampening filter'.
- Keep adding keyword rich content to your website.
- Purchase an already existing domain if possible - ensuring it was not banned by search engines earlier
You can check this article on
Google Sandbox for detailed discussion of Google sandbox.