Cell phone in Spain

I haven't used an eSIM in Spain, but I've done so in many European countries. It should be no problem at all. I get my eSIMs from Airalo, whose instructions I've found to be reliable. There may be slightly less expensive options from other countries, but you'll probably save a lot of money compared to what our US provider charges.

Most eSIMs provide only data. You can find eSIMs that allow cellular calling, but you'll have a different telephone number.

You mentioned that your trip is six months long. I trust you are aware that folks traveling on US passports without long-stay visas are limited to spending 90 days within any rolling 180-day period in the Schengen area. That area covers most western and central European countries except for the UK and Ireland. It's not terribly easy to spend six months in Europe and keep the Schengen time to no more than 90 days.

Orange Travel eSim worked for us in Spain (as well as Portugal, France, Germany and UK).

The nice thing about Orange is that it gives you a (French) telephone number to allow you to make unlimited calls and texts throughout Europe, in addition to mobile data. It even provides some limited long distance minutes and texts to call home.

You can register the number for a long stay and top up your plan as needed, but I have never done that. Good luck.

If you'll be in Spain for 6 months, I'd recommend getting a Spanish phone plan at a bricks-and-mortar shop after you arrive. You'll save a lot of money over an Orange plan you'd buy online, plus you'll have a Spanish phone number. If you need a little data for the day you arrive, you can buy a ~2-day data-only plan online for cheap. See esimdb.com.

I Will go to Spain next month, and I Will chose Orange, It Works well for France and Spain. Other option is Movistar, the Spain local company