Purchasing a partial Google Apps for Business account
Google Apps does not support both Google Apps (free edition) and Google Apps for Business user accounts on the same domain. You can only sign up or upgrade your entire domain to Google Apps for Business, and you'll need to purchase the upgraded service for every active user account at your domain.
If you don’t want to upgrade all of the existing accounts at your domain, you can delete any extra user accounts in your administrator control panel. By default, we’ll upgrade only active users - not the full number of accounts approved for your domain.
If you wish to purchase additional user accounts, you can do so when you upgrade your domain, or by clicking 'Buy more user accounts' at any time in Google Apps for Business. Details on purchasing more accounts.
If you're looking for a way to create more email addresses without buying another user account, keep in mind that you can add nicknames, email lists, and domain aliases free of charge. This allows you to send and receive mail from a variety of email addresses. Alternatively, you can create a new subdomain as a Google Apps for Business domain (for example, firstname.lastname@example.org) and use it to manage an equivalent account in the Google Apps (free edition) domain theurbanexperience.org.
Another option is to implement an email gateway. This setup gives you the option to have mail for some or all users sent to BOTH Google and your existing internal service.
In addition to the options above, the partner network can assist you with various email delivery settings, such as dual deployment, and our partners advertise their services in the Google Apps Marketplace.