Sellers can't start a chat or call with you. Contact must be made by you, the buyer, first. Once the chat has started, whenever a seller sends you a message you'll be notified by email, sms or a push from the app.

Here's a quick safety tip:

Once you've found the perfect item for you on OLX, make sure to meet the seller in a public location. Take your time to look over the item thoroughly before you hand over any money.