Telephony is becoming more and more inherent in packet switched networks in contemporary telecommunications environment. Many call control applications are present on the market offering new services. Different protocols are used for that purpose, although one is leading the battle in IMS standardization. SIP (Session Initiation Protocol) was proclaimed as standard signaling protocol. From online charging system perspective, the non-standard protocols caused only new problems, whereas the introduction of the standard ones has made development much easier. Because SIP protocol has not been created for telecommunications industry, standardization will not eliminate such issues. In the process of charging calls, the system could still be out of a call, and in that case does not controlling the call. Characteristics to the SIP, namely signalization and media stream possessing different channels and different paths, calls could be overcharged or even not charged at all. Charging issues are very sensitive, especially those ones referring to an online charging system responsible for call control. Case study model of the online charging is implemented in the JAIN SLEE environment. Communication with IMS core is being conducted through SIP/ISC interface. Charging system used in the laboratory model is the same as the one in a real network in commercial exploitation. Practical part is dealing with issues depicted in the theoretical part of this paper and possible resolutions on these issues.