This is a one-to-many situation, one client-to-many conversations, which means that it's the classic scenario for a Form/Subform.
The main table/form would hold fields for client ID, client name, contact information, and so forth.
The subform/subform table would hold fields for client ID, a conversationID, plus the fields you listed in your original post.
The form/subform would be linked by the clientID field.
A subform is usually either a Datasheet or Continuous View Form. Unless your notes will 256 characters or less (the max for a standard Text field) you'll have to use a Memo field. From a practical standpoint, if you use a Memo field you'll probably have to use a Continuous Form for the subform.
Alternatively, you could use a form/subform/subsubform configuration, with the subsubform holding the conversationID and the Memo field for the notes. The subform/subsubform would be linked by the conversationID field.
If you use this latter approach, I'd make the subform a Datasheet View Form and the subsubform a Single View Form.
I'd place the subsubform directly under the subform, so that as you scroll down the conversation records in the subform,the appropriate Notes would be displayed in the subsubform.
It's kind of complicated, but it's the scenario you've presented.
Hope this helps!
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007