What cell phones and plans available in korea?

He can bring a phone from the States and it should work fine as long as it is unlocked and he can get a plan there. The plans are reasonable

Also WiFi is everywhere in Korea she probably won’t have an issue reaching him.

If he’s taking an unlocked phone, he should be fine with getting a local SIM card in Korea. The major providers like KT, SK Telecom, and LG U+ all have reasonable plans, and their WiFi coverage is incredible. I’ve known people stationed there who just relied on WiFi and messaging apps like WhatsApp or iMessage to stay in touch with family back home.

For international calls, especially if he ever runs out of data or needs an affordable way to call family, getting a prepaid calling card could help. Services like https://paynet.red/ offer calling cards that work well for international calls, which might give his mom peace of mind.

I believe I had KT, no difference really from LG. They come with WiFi hotspots that are insanely good you don’t really even need to buy WiFi separately. You will need an unlocked phone (so paid off). My wife and I had no issues texting/calling to and from my Korean numeric number. iPhone to iPhone in the states to korea will still be iMessage compatible.

Korea has LG and KT for cell carriers. I brought my iPhone from the US with me and bought a SIM card and plan from the PX. It works perfectly fine. I am able to FaceTime with my family with no issues. The Korean phones are more expensive because they make you buy the phone and pay it off within the one year we are here. So if you buy the most expensive it may cost a couple hundred a month to pay it off. I know if he and his mom both have apple they can text all day without it charging extra normal calling can be done but it will cost extra after so many minutes. They will be able to keep in touch while they are away.