HONGKONG Telecom CSL will sell a second videophone, which is incompatible with the one it launched late last year, in a move it admits may cause some confusion. Later this month the company will start selling the videophones made by AT & T of the US alongside those made by GEC-Marconi of the UK. The two cannot make video calls to each other as they use differing methods of squeezing video signals down a telephone line. Hongkong Telecom CSL spokeswoman Ady Leung said confusion was one of the concerns the company needed to address. ''We want to make sure that the customer knows about the different standards,'' she said. The company has gained exclusive sales rights to both lines of equipment. The AT & T Videophone 2500, which can communicate with AT & T machines sold in the US, will sell for $7,988 during a promotional period. The GEC unit, whose price will rise to $5,998 at the end of this month, will talk to similar units being sold by British Telecom and MCI of the US. Both have similar-size screens, a similar casing design and send both sound and colour pictures through an ordinary telephone line with no extra call charges. AT & T's machine is black, GEC's light grey. Ms Leung said the company so far had sold ''a few hundred'' of the GEC videophones, blaming the manufacturer for not providing enough equipment to satisfy consumer demand. She said there would be no problem with supply of the AT & T equipment, which was launched in the US last August. Both have the useful function of being able to switch off the video link if necessary.