Android smartphone technology is growing rapidly. It is indicated that by utilizing the features of internet telephone service via the Voice over Internet Protocol (VoIP), users are able to make conversation easily and inexpensively. However, with the development, the internet telephone service used is unnecessarily safe for use. One of the solutions proposed is to make end-to-end encryption. This research applied TEA algorithm for encryption into the VoIP client of Sipdroid in Android smartphones. The objective of the research is to find out the effect of the application of TEA algorithm for encryption into the VoIP client of Sipdoid by investigating the performance of TEA algorithm in view of mean opinion score (MOS), delay, and throughput in VoIP. The results of measurement and calculation show that the application of TEA algorithm produced quality speech with R factors of 72.11676-75.01362 smaller than no TEA algorithm application with those of 84.79064-85.38539. Meanwhile, the effect of VoIP performance on such application generated a much larger delay of 0.018084 to 0.024327 seconds compared to no TEA algorithm application with a delay of 0.006071458 to 0.009465105 seconds. The results indicate that the application of TEA algorithm could more effectively contribute to the security of VoIP client practice, particularly in Android smartphones.