With a free jailbreak app- iTransmission now you can easily download torrents on your iPhone and its very similar to the one which you are using for your desktop or laptop. Yes, you are right i am talking about utorrent.
iTransmission is currently in alpha version and you can download it for free from the InsanelyI Cydia repo (repo.insanelyi.com)
When viewing an individual transfer in iTransmission, you are given plenty of information. You can see your download and upload speed for each individual transfer, as well as information like data received, sent, etc.
When a downloaded is completed, you’ll have the option to either remove the torrent itself or also remove the data associated with that torrent. If you want to keep what you downloaded, keep the data. You can use iFile or another SSH tool to grab the file later.
iTransmission is a nice app for downloading torrents directly on your iPhone. The project is open source. You can check out the Google Code page for more information.
To download iTransmission for free, add this repo in Cydia: http://cydia.ccp.li/
The other way to download torrents on iPhone is using the app IS Drive.