Nowadays, GSM Network has been deployed all over the world, including in Indonesia. Some GSM operators in Indonesia get prepared to develop their GSM networks toward GPRS. After GPRS, the next generation technology is Universal Mobile Telecommunication Service (UMTS). UMTS is a third generation of mobile telecommunication technology that is defined in ITU specification as International Mobile Telecommunications-2000 (IMT-2000). GSM/GPRS operators that want to deploy UMTS will wish to reuse the components of its existing network to the greatest extent possible. There is a significant opportunity to reuse existing equipment because of the fact that the core network of UMTS is essentially the same core network as is used for GSM/GPRS. 3GPP Release 1999 network architecture reuses a great deal of GPRS functionality for its packet data network. In this paper, we design an implementation planning of UMTS on existing GSM network. We use some network data of PT Telkomsel in Batam Area as our case study.