There seems to be a misunderstanding of the word "unlimited".
The industry uses it as a buzzword, but it is mostly a fake. Only very few countries actually still have real unlimited data rates on prepaid SIMs.
Given the fact, that data on roaming is given out for a price on average 20 times as much as domestic, real unlimited data rates for roaming do not exist in the EU. They are simply too expensive. Even Three UK's roaming offers are NOT unlimited.
To tell you the truth: I don't exactly know what you mean with unlimited:
- all "default rates", even the EU cap at 23 ct per MB are theoretically unlimited, as some poor fools had to notice facing horrendous bills.
- of course, the are "unlimited" rates governed by a Fair Use Policy. So you will be throttled having reached a certain high speed quota. Theoretically, data on these "unlimited" are really "endless", but throttled. I don't want to call this neither "flatrate" nor "unlimited".
Real unlimited unlimited rates for data on EU roaming with eat as much as you can in high speed do simply not exist, as they would cost a fortune.
-------------------------------------------------
Correction to Lover08: Thanks for loving my suggestions
But Orange Spain is not on 4G/LTE, not in Spain, nor anywhere else on prepaid.