US-based private equity investor Providence Equity Partners has invested $640 million for a 20 per cent stake in Aditya Birla Telecom Limited (ABTL), a wholly owned subsidiary of Idea Cellular. ABTL owns service licences for the Bihar and Jharkhand circles but, according to industry sources, the main attraction for Providence to acquire stake would have been access to Indus Towers through ABTL. The deal, which is subject to regulatory approvals, is expected to close by August 2008.