No, a definition of a context might be, e.g. in thefreedictionary.com -- I just double-clicked the word in Firefox with Dictionary tooltip extensionjenter;71821 said:If I recall correctly, the definition of a context is a set of actions that you physically can do now. So, in a way, if I can change my location, all the actions there can be considered to be in the same context.
2. The circumstances in which an event occurs; a setting.
Also, David Allen defines it on pg. 143 of his book as either the tool or the location or the person needed to complete an action (I would add "or the combination thereof).
So if you think about it, you could see various possibilities to define your own contexts, e.g. @Calls-Fred might be a possibility regarding your previous example. Also you may try @Calls-demanding and @Calls-other (I am using @Calls here in order to avoid any potential shortcomings of @Phone). The same principle would apply to Internet researches. Take some time to figure out which contexts suit your working style best and give them a try.
It's important to realize that you have to be in a context to complete an action, but you don't have to complete an action if you are in a particular context -- from your questions, it seems you are alluding to the latter, which is IMO an incorrect interpretation of GTD (I think others have made the point here as well).