Whether you’re just visiting on a tourist visa, or have moved permanently to Chile and are waiting on your residency application to be approved before you get a RUT number, you’ll probably want a phone plan of some kind while you’re in Chile. A quick internet search will tell you that in order to do this, you’ll need a RUT number, a Chilean ID number similar to a Social Security number in the US. However, there is a way around this. At least for the larger phone service providers—Movistar, Entel, Claro, and WOM—you can purchase a prepaid SIM card and have it set up with your passport number instead of a RUT. I don’t know that smaller/more local services allow this, but you can always ask. In order to switch SIM cards you'll need a phone with an unlocked SIM; if you don't have one, you can just buy a cheap one that takes SIM cards from any provider. The setting-up process will be smoother if you purchase the prepaid card directly from the provider’s storefront, but SIM cards from various providers (most commonly Movistar, Entel, Claro, and WOM) are available in most minimarkets and even some of the more informal restaurants. If you’re having trouble setting up your SIM card and the person you purchased it from isn’t sure how to do it without a RUT number, just try to find another store that sells these cards and ask for help there; or better yet, find the storefront of the service provider and inquire at the helpdesk.
Once you’ve gotten your number set up, you can refill the balance on your account just about anywhere. One option is to do it online, but that seems to be a little glitchy at times for foreign credit or debit cards. The most common method is by cash at a minimarket or a kiosk. Both of these are just about everywhere, including bus stations and malls. Just look for a sign that says “Recargar” or “Recargar Telefono” with the service providers’ symbols. In order to put more money on your account, you just have to tell the person at the counter your phone service provider, phone number, and how much you’d like to put on your account. They’ll dial your number and the amount you’re adding to your account into the card processor and you hand them the cash for whatever amount you told them. It’s possible to use a credit or debit card, but for security reasons cash is a better idea—having your card number stolen is rare, but most of the card processors are not very secure and it’s better to avoid using them if possible.
After you’ve refilled your balance, you can dial a 3-digit number to listen to the options and select a “bolsa prepago”, a prepaid package. These can be packages that are just for more data, or that include both minutes and data, and are valid for set amounts of time (2 days, 7 days, 15 days, etc.). The packages are fairly inexpensive—the various providers are competitive and price points are comparable among the companies. For instance, a couple of the packages Movistar offers is one with 500 MB+60 minutes+60 SMS, valid for 7 days for 2,000 CLP (about $3.30 USD) or 1.5 GB+100 minutes+100 SMS, valid for 15 days for 5,000 CLP (about $8.30 USD).
For Movistar, dial *303#