Any idea on how much those nano sims run and how much data they offer? From what I have read it seems vodaphone is the big carrier there.
Vodafone is the best, in terms of quality of the support services. TMN is the biggest, but is not the best.
Optimus is the small one, so it has the best prices (+/-, since the all more or less have the same prices.. they copy each others prices ).
But in terms of qualitiy of the technical services and coverage they are all good. TMN is a little worse because since the majority is TMN in the crowed areas the quality decrease.
I would recommended you one of this 2:
http://www.optimus.pt/Particulares/Movel/Tarifarios/Prepagos/Detalhe/SmartPre
12euros month, with 400megas internet and 80 free SMS/MMS.
In vodafone, maybe this option:
https://loja.vodafone.pt/tarifarios/aditivos/internet/?ecmp=mdd
This is just the internet option, but you can buy a card without mandatory charge and use the money only to pay net.
If I am not wrong, all the card's cost Xeuros with Xeuros included.
If you need any help, I'm portuguese ( but currently living in Germany ) just ask

.
Have fun around there
