Using Outlook
I often seem to have this sort of task which is of the 'sometime this week' variety. I tend to use one of two methods, depending on the significance of the call. In many cases I simply use a dated task entry in Outlook with a suitable deadline reminder for the end of the week built in. However, if the commitment is particularly important, I tend to drop it into my calendar for the soonest day I am able to make the call. This tends to help me either keep my commitments at the earliest available point or allows me to drag the task appointment to the next day if necessary. I find this choice of two approaches let me treat the call either within the flexibility of a task list seen at least daily or more rigidly as a 'hard landscape' item if I want to ensure it gets priority treatment on a particular day. Does this help (assuming you are using Outlook or similar!)?