This paper analyzes the Improved Cellular Message Encryption Algorithm (CMEA-I) which is an improved version of the Telecommunication Industry Association's Cellular Message Encryption Algorithm (CMEA). We present a chosen-plaintext attack of CMEA-I which requires less than 850 plaintexts in its adaptive version. This demonstrates that the improvements made over CMEA are ineffective to thwart such attacks and confirms that the security of CMEA and its variants must be reconsidered from the beginning.