Tip: to reduce fees and added charges, consider obtaining the SIM in the country where you will spend the majority of your time. There WAS a plan to harmonize cellular rates across the EU.
I do not know if this happened. If it did, it makes the EU one big market for cellular billing purposes. So, for voice and probably text, there would not be different charges when using a French SIM in Spain, or vice versa.
My recollection from when I used to use foreign SIMs and older cell phone is that there were added costs to make calls in Spain or Portugal with a French SIM and vice versa.
Then again, my recollection could be all wrong and out of date. I do not mind being corrected.
Personally, I use t-Mobil here in the US. They give me unlimited free text and data in 140+ countries worldwide. So, when I go to Spain to walk Camino or work as a volunteer, my phone fires up and joins Orange, Movistar, or another European network automatically as soon as I land in Europe. This works the same across the EU.
t-Mobile charges USD 25 cents per minute for voice calls. So, if my phone rings in Europe, I answer and tell the person to text or e-mail me, or that I will call them back when I can make the call over Wi-Fi. In a month, I might get charged only a couple of dollars for a few incoming calls. I only make outgoing calls to friends or family when I can do so over free Wi-Fi.
Hope this helps.