I've been looking around mobile plans recently and this one came to my eye. It's pretty rare to find a $40 unlimited plan which includes a handset, also 4 GB data. If you are looking for a handset or don't mind the 24 month contract this could be a winner.
There are probably better plans for $40 but this may suit you as they don't include a phone.
Edit:
Phone details: http://www.gsmarena.com/alcatel_idol_3_(5_5)-7081.php
http://www.gsmarena.com/alcatel_idol_3_%285_5%29-7081.php