New types of mobile phones branded as dual band have recently hit the mobile phone market. As the name implies, these telephones operate on two GSM system frequency bands. Both on the 900 MHz frequency band on which all GSM mobile phones in the Czech Republic currently work, and on the 1800 MHz frequency band which is familiar to us for the meantime only from the experience of some foreign operators. To look at, dual band mobile phones don't differ at all from existing GSM mobile phones. As long as a given operator operates its mobile telecommunications network on two frequency bands, switching between the various bands takes place automatically when needed and without the knowledge of the latest dual-band telephone's owner. One of the reasons why EuroTel is beginning to offer and to sell the newest dual-band telephones is the assumption that licenses for operating mobile telecommunications networks in the 1800 MHz band will be granted during next year. Several of this band's channels are to be allotted to EuroTel which plans to utilize them in order to expand the capacity of the existing GSM network. This dual-band system can, however, be expected to be introduced at the beginning only at locations with a large density of mobile phones, being primarily in large cities. The main and indisputable advantage of introducing this system is primarily the increase in the 900 MHz GSM network's capacity and the related connection quality increase through reducing the number of blocked calls. Owners of dual-band mobile phones will appreciate another of their mention-worthy qualities especially on trips to EuroTel roaming partner countries-mobile telecommunications network operators in the 1800 MHz band. That is to say that a lower calling fee rate can be expected for using these operators' services than from a GSM 900 MHz network operator. Today, we would like to introduce you to at least two mobile phones which support this technology-the Nokia 6150 and the Ericsson SH 888.