Getting through to some businesses can be challenging, to say the least. If your customers are phoning with a specific inquiry that may take more than a few minutes for you to deal with, offer to call them back rather than making them wait on hold.
I have done a lot of research on customer service and, without doubt, when it comes to the most common complaints, failing to return telephone calls is up there near the top of the list. So, if you offer good customer service by telling your customers that you don't want to keep them waiting on hold, make sure that you follow through and call them back quickly.
I know what it can be like when things get busy around the workplace. It's easy to get sidetracked and diverted from your mission and your responsibility to your customer, but if you say that you will call them back, make sure that you do. If the customer's request is going to take longer than you first anticipated, give them a call and let them know that you are working on it and that you should have an answer by a certain time. Think back to those times when you have waited for a call back from a supplier, only to have to chase them up time and time again. Are you likely to want to deal with them again in the future?