It is every parent’s nightmare: Your child is going off to study abroad. As unsettling as that might be, the real nightmare comes when you get your first cellphone bill and realize you forgot to address the issue of staying in touch.

In truth, it’s not just kids; it’s anyone who travels with a smartphone. Student or senior citizen, you need to address communication needs well before takeoff.

Here’s a step-by-step guide:

Step 1: Find out whether the cellphone that will be traveling abroad can be unlocked — that is, untethered from your carrier. Generally, if your phone is paid for, it can be unlocked, so skip ahead to Step 2.

If you still owe money on your phone, it can be unlocked, but you must pay off the contract. If you choose to pay it off, go to Step 2.

If you choose not to pay it off, go to Step 3.

Step 2: An unlocked phone means you are no longer in an exclusive relationship with your carrier and you can start dating other carriers.

That means the next move is to consider buying a SIM card for the area or country being visited.

You’ll get a local number. Depending on the plan you choose, you’ll have data and all the perks of your phone at home. But let’s say you like your carrier. Go to Step 3.

Step 3: You have decided not to break up with your carrier, so you’re keeping your phone locked. Or the financial disincentives mean you must stick with the carrier. In either case, you must protect yourself financially.

You have two options. Sticking with your carrier, go to Step 4, Option A.

Moving your phone service elsewhere, go to Step 4, Option B.

Step 4: >> Option A: If you’re keeping your phone and it’s locked, you should consider an international calling plan from your carrier that offers talk time and data.

You can burn through a lot of data quickly, so choose a plan accordingly. Skip to the section titled “Keeping costs down.”

>> Option B: You know how people sometimes buy an old beater truck just because they hate mucking up their regular car?

Say hello to the concept of a beater phone.

You can go to Amazon, eBay or pretty much any other phone-selling site and buy an unlocked phone. It may not be quite as nice as the phone you have, but it won’t cost you the family fortune, either. If this is what you choose, see Step 2 about buying a local SIM.

Also, see our video about replacing a SIM card at lat.ms/changeaSIM.

Keeping costs down

Kimberly Palmer, a credit card and banking expert for NerdWallet.com, and Jennifer McDermott, a consumer advocate for Finder.com, endorsed Skype and Whats App, as did colleagues in the travel communications business.

Here’s what almost everyone agreed on:

>> Skype: You don’t have to have a smartphone to use Skype, although you can call using Skype from a smartphone. But you also call from a laptop, a tablet, even an iPod if it has Wi-Fi and you have the app or a way to log in to Skype.com.

If your student has Skype and you have Skype, the cost of a call is free when you Skype to Skype.

If you originate the call and the callee isn’t using Skype, the cost to you is usually 2 or 3 cents a minute, more if you’re calling a cellphone.

Wi-Fi is imperative in either case.

>> WhatsApp: It began life as a messaging app but has grown to include voice and video calling.

An added feature, said Albert Stumm, a travel writer based in Barcelona, Spain, is that it “uses very little data for its voice call function, so I never worry about using it in my cellular network’s plan either.”

And parents, here’s an important consideration: “It’s also the app that young people use almost universally throughout Europe to send text messages,” he said in an email.

Other thumbs up went to Apple’s Facetime (although it takes some bandwidth) and Facebook Messenger; both offer voice and video. Then there’s MagicJack, free as a phone app but not by PC.