I assume you are using dictionary managed tablespaces. You have to wait until all extents are deallocated. The following statement should report the number of extents that are to deallocate:
Index segments and materialized view logs have to be deallocated too, if they exist.
If you drop and recreate the table you will have to wait, too. Dropping the table will take as long as truncation of the table because the number of extents to release is almost the same.
Maybe the following will help:
instead of drop and recreate you
1) rename the table TABLENAME to OLDTABLE
2) create a new table with the original name TABLENAME. Now you have an empty table TABLENAME
3) you drop the table OLDTABLE
The advantage of this approach is you can continue your work with table TABLENAME after step 2. But the space occupied by the former table TABLENAME will be release during the execution of step 3.
In Linux you can start the job that does step 3 in the background with nohup so that you must not leave your terminal window open. Use
nohup sqlplus user/password@tnsname @dropscript.sql &.
Even if you want to restart the database during execution of step 3 this is not a problem because Oracle can handle such situations.
As far as I remember it does this in the following way:
After the restart of the instance (or if the sessions that does the drop of the table dies for some other reasons) the segment of the table is converted to a temporary segments. Its extents are deallocated by a background process (I think it is smon). The table is removed from the dictionary after the death of session so the tablename OLDTABLE is not visible in the dictionary anymore.