Foreigners who intend to stay in Italy for a short vacation or for a longer period of time, can get an Italian mobile phone number (rechargeable sim card) just by going to one of the mobile phone company stores (e.g. Tim, Vodafone, Wind, Tre, Fastweb) with a valid passport. Otherwise, foreigners, who have all the required documents, can ask for a monthly payment plan.
How to get an Italian mobile phone number
If you are a foreign citizen who intends to stay in Italy for a short vacation or for a longer period of time, you can get an Italian mobile phone number just by going to one of the mobile phone company stores (e.g. Tim, Vodafone, Wind, Tre, Fastweb), which you can find almost anywhere throughout the city, and asking for a sim card.
While you are in Italy, an Italian phone number is useful not only for making regular calls, sending text messages (sms), or surfing the internet at a cheap price, but often for opening a bank account, or for dealing with public administrations, institutions, service providers (energy, gas, light, internet, etc.), public and private companies (e.g. insurance companies), etc.. Some of the aforementioned prefer to communicate via text messages.
It is possible to ask for a rechargeable sim card or, if all the requirements are met, for a card with a monthly payment plan.
Rechargeable Sim Card
It is very easy for a foreigner to obtain a rechargeable sim card with a regular Italian phone number. As a matter of fact, foreigners can get an Italian phone number just by going to one of the mobile phone company stores (e.g. Tim, Vodafone, Wind, Tre, Fastweb) with a valid passport.
The provider will give you a sim card that will be associated with a calling/data plan, that generally includes a certain number of minutes, text messages (sms), and Gigabytes per month, for which you will have to pay (i.e. recharge the card) a determined sum every month (currently prices are around € 6-15 per month). It is generally possible to recharge the card at tobacco shops, supermarkets, company stores, online or via app.
If you want to keep the card active and use the offer that you signed up for you must recharge it periodically (generally every 4 weeks) before your monthly offer expires, and at least once a year otherwise the sim card will expire. So, you can keep recharging the card every month until you need it.
If you do not recharge your card, it will remain active for 12 months and you will be able to receive incoming calls or text messages, but not to make outgoing calls, send text messages or surf the internet. After 12 months from the last recharge, the sim card will expire. Therefore – considering that, while you are in Italy, it could be cheaper to use an Italian phone number with its calling/data plan, rather then your national one – if you need an Italian phone number for a short period of time, or if you do not want to spend a lot of money or be bound for years to a phone company, a rechargeable card is probably your best solution.
As a matter of fact, rechargeable cards are very popular among Italians them selves.
Sim card and monthly payment plan
It is also possible to sign a contract with the provider (e.g. Tim, Vodafone, Wind, Tre, Fastweb) that gives you a monthly payment plan. This means that the provider offers a calling/data plan, that generally includes a certain number of minutes, text messages, and Gigabytes per month, for which you will have to pay a determined sum every month, for a pre-determined period of time (generally 24/30 months).
The difference with the rechargeable card is that, while with the rechargeable card you can decide if you want to recharge it or not, with this kind of contract the company will charge you the sum you agreed to pay every month, by automatically withdrawing the money from your credit card or bank account, for the entire duration of the contract (24/30 months). As a matter of fact, if you withdraw from the contract before its expiration you will have to pay the remaining installments in addition to a penalty.
This type of contract is widespread among Italians, especially because it allows customers to include the purchase of a smartphone in their contract for which an additional fee (generally € 0/3/5/10/20 depending on the phone) will be added to the monthly payment (for the calling/data plan). This way it is possible to acquire an expensive smartphone by paying for it in monthly installments. Currently, it is possible to sign a contract that includes a certain number of minutes, text messages, and Gigabytes per month, plus a smartphone, for a total of € 15/20 per month.
In case of a monthly payment plan, in addition to the monthly amount you may have to pay the Government Concession Tax (€ 5.16 per month).
However, in order to sign a contract as described above, you will need:
1) passport;
2) codice fiscale (the Italian tax code);
3) permit of stay (depending on your country of origin);
4) Italian credit card (which means an Italian bank account and, therefore, you will also need to be registered as a “resident” in the Municipality (“Comune”) of interest. Non-resident bank accounts are generally not accepted).n1
Activation costs
Some companies activate your new phone number (sim card) for free, while others will charge an activation cost that usually goes from € 5 to € 30.
Major Italian phone companies and calling/data plans
Major Italian phone companies are Tim, Vodafone, Wind, Tre, Fastweb (Wind and Tre have recently merged so soon they will be one company).
The specific pricing/calling plans for foreigners change from time to time, but are quite similar among the providers. For example, major phone companies are currently offering 1000 minutes (of which 300 to call your country) + 3 Giga at a cost of € 10 for 4 weeks (some companies include text messages some others do not).
Where to buy a mobile phone
Having said the above, if needed, it is possible to buy smartphones in the phone company stores, supermarkets, specialized stores, major nationwide tech stores like Euronics, Media World, Unieuro, Trony, etc. on their websites or online at Amazon, Ebay, etc.. You can find them everywhere and special offers are always on!!

David
Very welcome and useful information. Would appreciate a similar post for internet providers.
How about buying the SIM card online, prior to traveling, and getting it mailed to the US?
A lot of times, one needs to provide a phone number (an Italian one), in order to coordinate formalities prior to actually get there.
Thank you