The area codes for Denver and Boulder are 303 and 720. In Colorado Springs, it's 719. In Denver and Boulder, the full 10-digit phone number is required to make local calls, whereas the area code is not necessary in Colorado Springs. Most convenience stores and supermarkets carry calling cards for national and international calls. Pay phones still exist in the area, but their numbers have been on the decline in recent years. However, they are readily available in the downtowns of all three cities.
All major U.S. cellular networks work fine on the Front Range, but things quickly get spotty outside of the urban cores. If you're not from the U.S., you'll be appalled at the poor reach of the GSM (Global System for Mobile Communications) wireless network, which is used by much of the rest of the world. Your phone will probably work in most major U.S. cities; it may not work in many rural areas. To see where GSM phones work in the U.S., check out www.t-mobile.com/coverage. And you may or may not be able to send SMS (text messaging) home.
Voice Over Internet Protocol (VOIP)
If you have Web access while traveling, consider a broadband-based telephone service (in technical terms, Voice-over Internet Protocol, or VoIP) such as Skype (www.skype.com) or Vonage (www.vonage.com), which allow you to make free international calls from your laptop or in a cybercafe. Neither service requires the people you're calling to also have that service (though there are fees if they do not). Check the websites for details.
Internet & E-Mail
With Your Own Computer -- Wi-Fi is readily available at hotels and hundreds of public places in Denver, Boulder, and Colorado Springs, including Denver's 16th Street Mall. For specific spots, check out the website www.jiwire.com.
Without Your Own Computer -- Most major airports have Internet kiosks that provide basic Web access for a per-minute fee that's usually higher than cybercafe prices. Check out copy shops like Kinko's (FedEx Office), which offers computer stations with fully loaded software (as well as Wi-Fi).
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.