Ringio can sync contacts with one of your Google Contacts / Gmail contacts / Google Apps for your domain email contacts. If you have more than one gmail account, and would like to see all of those contacts in Ringio, here are current workarounds:

A)  Make one your "master contacts account". Export your contacts from the "less important" accounts using the "Export" link in the Google Contacts interface, then import the resulting files to your "most important" account,  then sync with Ringio using that account.

B) Export all sets of contacts then import them both into a fake contacts-only gmail or Google Account (google.com/contacts)... but then you will be two way syncing to something that you don't look up anywhere.

I've taken approach A myself.