Telephone Rentals Plc, itself a perennial subject of bid speculation, has taken a 15% stake in Carphone Group Ltd, which has been a major beneficiary of the cellular mobile telephone boom, and has now signed 13,500 subscribers. Telephone Rentals is paying UKP825,000 for the 15% stake, and Carphone has issued UKP400,000 of paper convertible into 5% of the equity to Lloyds Development Capital. The company, previously privately-held with all the shares in the hands of chairman Graham Thomas and his family, is forecasting sales of UKP30m in the financial year just started, up from UKP17m in the year to March 1987. It has expanded by acquisition of smaller rivals as well as by internally-generated growth, and plans to use the cash to make more acquisitions and to expand into overseas markets. Telephone Rentals already had a joint venture with Carphone to distribute cellular telephones, and wants to expand its mobile communications business further.