Should call the listing agent when I find a home I like?

You absolutely can call the listing agent or you can call any agent you would like to represent you on the buyer side of things. You may prefer a different one than the listing agent so that you are their only client in the transaction.

There are a couple of things to consider here. Yes you can call and use the listing agent but only if they are allowed to be what is called a dual agent (represent both sides, if allowed in your state and by the seller). They will not be able to fully help you with determining what price to offer, negotiation strategy etc, but can help you write the offer and present that to the seller and manage a transaction to closing. A dedicated buyers agent could be fully on your side in terms of finding comparable properties, pricing, negotiation strategy, and getting it to closing. Hope that helps.