Motorola Defy does not sync to GMail

I have purchased a Motorola Defy some time ago, and imported my address book from my old featurephone using the SIM card. Under Settings / Account now I have two accounts listed in the Motoblur section (the motoblur account and an email account), and one account listed under Other accounts (the gmail / google account). Now I would like to sync all contacts to the google account, but it won't: it has synced only the new contacts I added, but the old contacts are in the telephone only. What is the correct way to sync contacts to the gmail account? I am running official froyo firmware, french version.