As an expat, absolutely nothing. It drops off the credit report after 7 years.
Now before everyone gets indignant. I was a Verizon customer and had taken a job abroad. 18 months into my 2-year contract I called to say I'm leaving next month and want to cancel. The fuckers wanted to put me on a 2-month pause, stop the line for 2 months add 2 more months on the contract. I told them this was a permanent move and I didn't want to bother, just shut it down. Then they wanted to hit me with a $250 cancellation fee, not prorated. I referenced the part of the contract about coverage but the rep wasn't hearing it. While at the airport I called them and paid my final bill (they charged me to pay by credit card over the phone, too). Told them to cancel the line and goodbye.
I got a few very large bills in the mail after that, a few creditors calling my Google voice line, and then silence. It's been that way for 6 years.
A few years ago, when I moved overseas, T-Mobile had no trouble waiving the termination fees (for both my line and my wife's) once I'd shown them proof of the move. And they'd already unlocked our phones for a previous international trip, which was handy because we could easily go prepaid until we picked a carrier post-move.