I like this too. It shows that you're not out to gouge the customer which is a really important step. The main thing I like about it is that it will set expectations. The client isn't likely to know how much this new 'communication' charging is going to cost them because they don't have historical data to refer to. If you give them this gift card and they chew through ten hours in a month then they know what to expect going forward which they can either account for, or if they consider it too high they will find ways to minimise the amount of your time they use. Either way is a win.