The right tactics to avoid high cellphone charges depend on which network operator you use, the length of your trip and your destination.

First of all , decide on which part of the world you are travelling to . In Europe , GSM is the cellular technology used for operator like Cingular and T-Mobile while another technology CDMA cellular technology is used in United States for operator like Sprint and Verizon Wireless .However , the pricier part comes with international roaming….

with your home network which will able to automatically detect the visiting countries network but unexpected high cost of bill is determined by the length of calls as well as roaming destination distance.

Thus , the next immediate step is to unlock your GSM or CDMA phone to facilate insertion of prepaid local SIM(subscriber identity module) or removable smart card by making use local carrier or network as well as local phone number to give you a great deal savings.If not for the bandwidth compatibility , for example whether the phone is supporting 900 and 1800 GSM bands , an alternatively solution is to get hold of GSM/CDMA phones by rental.

To explain a little more technically on GSM and CDMA cellular telephony bandwidth system , here is :

GSM , short for Global System for Mobile Communications, one of the leading digital cellular systems. GSM uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency.GSM differs significantly from its predecessors in that both signaling and speech channels are Digital call quality, which means that it is considered a second generation (2G) mobile phone system. This fact has also meant that data communication was built into the system from the 3rd Generation (3G)

TDMA , short for Time Division Multiple Access, a technology for delivering digital wireless service using time-division multiplexing (TDM). TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels.

CDMA , short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM, that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.

In short , the Global System for Mobile Communications (GSM) standard is a specification of an entire network infrastructure, the CDMA interface relates only to the air interface—the radio part of the technology. For example GSM specifies an infrastructure based on internationally approved standard while CDMA allows each operator to provide the network features as it finds suited.


A majority of the world’s cellphone subscribers — 82 percent — use the GSM technology standard, according to the GSM Association. In the United States, the major network operators use two systems. Cingular and T-Mobile use GSM, while Sprint use CDMA, an incompatible technology. CDMA technology is found in North America, as well as some Asian countries, but it is basically nonexistent in Europe. As a result, Sprint and Verizon customers can use their phones in just 26 countries. (AT&T and T-Mobile customers can potentially use theirs in over a hundred.) Cingular and T-Mobile customers have more options — if their existing phones can pick up multiple frequencies. To complicate matters, the American GSM standard operates on 850 and 1,900 megahertz, while the rest of the GSM world uses 900 and 1,800 megahertz. To use GSM cellphone in a foreign country, the handset you own must be tri-band or quad-band and able to operate on one or both of the frequencies used outside the United States. Most of the operators Web sites list the predominant frequencies used in each country, and show if your phone can operate on one or both overseas bands.

A Temporary SIM Card
GSM phones use SIM cards (subscriber identity modules), tiny electronic chips that hold a cellphone’s “brains,” including the subscriber’s contact numbers and phone number. (CDMA phones store such information directly in the hardware.) GSM customers can avoid sky-high roaming charges by replacing their SIM cards with ones from other countries. For example, travelers to Britain can pick up a SIM card from the British carrier Vodafone; once inserted, it gives the phone a temporary British phone number. Calls within Britain and to the United States would be much cheaper. Another benefit when using overseas SIM cards is that incoming calls are typically free in most countries. Overseas SIM cards can be purchased before you travel from companies like Cellular Abroad or at local shops in foreign countries.

Unlocking the Phone
Even if you have a GSM phone that operates on both overseas frequencies, domestic cellphone providers do not want you to use your phone with another company’s SIM card, because they do not make any money when you do. To prevent your doing so, cellphones bought through Cingular and T-Mobile are electronically locked — they accept only their own company’s SIM cards.There are several ways to unlock your phone and avoid those high overseas roaming rates. Most operators will unlock their customers’ phones under certain conditions. Other GSM Phones Cellphone customers with dual-band GSM phones that cannot be used overseas can always purchase unlocked quad-band phones from third-party providers. Since they are unlocked, they can also be used instead of your current phone on your network. Because the phone is not subsidized by a carrier, the price is higher.

A Few More Tips
When entering numbers in your phone, always add the plus (+) sign and the country code; that way, the number can be dialed automatically no matter from what country you are calling. Store your GSM phone’s numbers in the phone itself, rather than the SIM card. Then the numbers will still be available to you when you use an overseas SIM card. To transfer them to a new phone easily, store them on a device like Backup-Pal (www.backup-pal.com), an external U.S.B. memory unit. While you will not pay any charges for incoming calls when you use a foreign SIM card, tell your callers to get an overseas calling plan from their phone company before you ask them to ring you. If they do not, they could be paying the same sky-high rates that you just avoided.