Covve currently syncs with all major address book accounts such as Gmail, Exchange, iCloud and Yahoo.
In order to to signup to Covve your device needs to have contacts in one (or more) of these sources.
Most people will have their contacts in one of these groups. If you don't then its likely that your contacts are stored directly on your phone or on your SIM card.
Covve doesn't work with SIM contacts directly. The reason is that SIM cards are simply, very limiting in terms of the data they can hold when it comes to contacts.
It is good practice to move contacts from your phone/SIM to an online addressbook (e.g. Google). This will make sure your contacts are never lost (e.g. if your phone is lost) and will also enable you to signup to Covve.