Most engineers aren’t directly involved with sales and marketing. Your opportunities to talk with customers come in the form of product support and feedback. Your company has forums, bug tracking systems, and other places where customers can ask question. You should be active on those forums so you can help your customers, increase your knowledge of how your product is used, and stay visible to other people in your company.
When the opportunity to support customers arises, don’t pass the buck. Helping a key customer out of a difficult situation is a great way to earn recognition with the customer and with your company. Helping customers takes time away from being a productive coder, but getting an important customer out of a jam is almost always worth it.
Take every chance you can to hear what your customers think of your products and what they want to see from them in the future. Engaging your customers in a conversation about your products will improve your product offerings, it also creates relationships with your customers. You may be in a different location, but you are part of the company and you want to make your customers know it.
The goal of interacting directly with customers is to create working relationships that make the customers happy. If a customer mentions you by name as a reason they like to do business with your company it will be a big help to your career.