Development of mobile phones has turned them into miniature computing devices which can be used for something more than simple voice communication. With the appearance of fast 3G mobile phone networks and unlimited data plans offered by operators it becomes more feasible to use them for long term patient cardio monitoring. We developed a system that consists of digital electrocardiogram recorder, Windows Mobile smartphone and personal computer. Electrocardiogram recorder is connected to the phone using cable or Bluetooth short range wireless link. Smartphone is connected to the Internet by means of mobile phone network and forwards incoming ECG data to the PC with software for data processing. We performed several experiments using different smartphones, different data transmission technologies and different ECG recorders to determine if it is possible to use this system for real time monitoring of patients electrocardiogram. In this paper we share experience while developing this system. One of the main problems is unpredictable number of users using the same mobile network and reducing the speed for others. Nevertheless, we can conclude that it is possible to transmit 12 lead ECG in real time using mobile phone.