Mine ring a bell. Loki learned in like 2 days. Sammy took a couple months to get it but she does it now. If she rings and we ignore her (because she rings for attention) she will bark at us if she really wants to go out.
Anyway, I have the Tell Bells on my website
Barkaholics — Welcome and Isabel on here has the hanging bells on hers
The Bows and Tails Boutique