Activity search by subject - advanced search vs activity search
You can use wildcard characters (%xxxx%) in search to change the default operator of "=" to "LIKE" - e.g. on demo:

Using Search > Find Activities:


Activity Text = Tell a Friend
Status = Scheduled, Completed
Generates the same query as you listed in your question and at the time I write results in 204 records:

Activity targeted to ...AND...

Activity Text (Subject Only) Like '%Tell a Friend%' ...AND...

Activity Status In Scheduled, Completed


The same query is generated when using  Search > Advanced Search with the following parameters:


Activity Text = %Tell a Friend%
Status = Scheduled, Completed


The above returns 89 contacts, but if you display the results as activities, you get the same 204 that you did using Search > Find Activities.

Hope this helps,
Tamar