(Telecompaper) Mobile towers operator Crown Castle announced it's considering a sale of its Australian subsidiary, after receiving unsolicited offers for the company. US-based Crown Castle owns 77.6 percent of CCAL, the largest independent tower operator in Australia. It entered the Australian market in 2000, acquiring towers first from Optus and later from Vodafone and Hutchison. The Australian company contributes around 4-5 percent of Crown Castle's estimated annual EBITDA.