In the German “hardware” section, there’s a topic about telephone ring indicators. For those that may need one - here’s the cheapest one I’ve found (and used)
http://sarabec.com/prodpage.asp?ID=39
These are quite a powerful units - and for those of you (like myself) who aren’t fond of having their picture taken - this one is no exception… I wouldn’t have it pointing directly at you, but angled away - If you’re on-air and it starts to flash, it’s a bit of an attention grabber!
…Oh hang on, that’s the idea 