Is caller already in the database?

Is caller already in the database?

This seems like a simple question, but we're new to Zoho. We run a home improvement company that gets lots of calls off our advertising, referrals, etc. We get a lot of repeat business, and when someone calls, we want to ask their name and see if they're already in the database. Ideally, we wouldn't have to enter it once on a search, then again to add them if they're not already there. 

I'm sure this isn't new ground here. What's the normal practice for doing this?