Use the preferences panel to change the names of certain fields and even to make them visible or not. You might want to change "Subject" to "Reference" or something else more relevant to you, or you might simply want to hide the "Spoke to" field.
A list of configurable categories is available for you to use to index your calls any way you want. Each call log can use different category lists — how you use these is up to you.
You can also assign a status to each call so that you can keep track of those that have been completed, need follow-up, are awaiting reply etc. The list of available statuses can be changed in the preferences and you can filter the call list for only those with a particular status.