Mobiltel AD, Bulgaria's only digital mobile phone company, said it's planning an initial public offering of its shares on a European stock exchange late this year or early next year, to be managed by J.P. Morgan & Co. and Credit Suisse First Boston. Mobiltel more than tripled its number of clients last year and earned revenue of about USD 180 million. The company plans to invest BGN 150 million this year to expand the network in the country and introduce new services. Mobiltel will face its first competition for digital GSM service after the government completes the sale of 51% of the Bulgarian Telecommunication Co. to the Dutch-Greek venture Royal KPN NV and Hellenic Telecommunications Organization SA. Currently Mobiltel's only competitor is Mobikom, a joint venture between Bulgarian Telecommunication Co. and U.K.'s Cable & Wireless Plc, which offers an analog-type cellular network. Mobiltel, which started up 1995, currently has 230,000 customers and is adding as much as 1,300 daily