Twitterfon
Twitterfon the iPhone twitter app
It is an awesome twitter app for the awesome iPhone, Twitterfon is a Twitter App which is made to make your work cut out on Twitter as you can see your friends/replies/messages timeline, see favorites, and send/reply a tweet.
You can also search tweets, get twitter trends, upload photos to twitpic.com, and update your location information.
This app i think is the best twitter app on the iPhone with is userfriendly interface it is a thing which even children can use very easily.
Twitterfon is Available in Free and the Pro versions.
Features for each one are
Twitterfon Free:

Price: Free
You can See
- Friends
- Replies
- Message timeline
- Favourites
- You can send Replies all in one go.
- Twitter Trends
- Saved Searche
- User Lookup
- Ticker Symbol for Stock Twits
- Conversation View
The free version has it all, i think free version has all the features which are useful in a happy and easy twittering then what the need is to look at the pro version whic is $5 more.
Twitterfon Pro:
Price: $4.99
You can See
- Friends
- Replies
- Message timeline
- Favourites
- You can send Replies all in one go.
- Twitter Trends
- Saved Searche
- User Lookup
- Ticker Symbol for Stock Twits
- Conversation View
The 7 additional features are :
- Multi Account
- 4 Themes
- Landscape Keyboard
- Shake to Reload
- User-Authenticated bit.ly
- Instapaper Integration
- Ad Free
So if you earn a lot and have loads of money to enjoy some additional features which is not so much different from the free version then just go for it to Shake to reload and other stuff like that which can be a good ones to show off.
Top 20 Social Networking Apps for iPhone
Linkedin: A valuable application especially for LinkedIn users. In our book, LinkedIn puts some business sense into the iPhone applications.

Skype: The famous online voice chating service on the web with millions of users is now available for the iPhone.

Facebook: The Number 1 soial networking site which is known as the best in the web, is just one click away in your iPhone download this app and have facebook just one click away on the move.

AIM Messaging: Mobile AIM lets you communicate whenever you want, wherever you are, in whatever way suits you best. Connect with friends and family and keep track of status and presence updates in real time.
iFlickr: The best photosharing site on your fingertips.
Youtube: Watch your favourite videos on the move and can even upload with the iPhone 3GS on the move.

Google mobile: If included with Google wave which is coming up this would be a must have app for iPhone.
MySpace: Myspace.com now on your iPhone now shows you an interstitial page where you can choose to use the mobile version or the full site.
Yahoomessenger: The good old Ymessenger which never gets old and keeps up with the modern trend into your iPhone.

Twitterific: This application lets you read and publish tweets on Twitter’s public timeline. It’s a great way to stay connected with friends, families and co-workers.

TwitterVision: This is a cool twitter app which works on geomapping the users and works with just one tap on the user to follow his updates.
Twitterfon: The twitter app which i din like much compared to the Twinkle but it can be tried out and might turn out to be someones favourite.
TypePad: the larget paid blogging service in the world is made easily acssible for iPhone users through this cool application.
Tumble: Twitter’s most efficient rival gets an iPhone application as well. It lets you post photos, quotes, links and more to your Tumblr account.
Instant Messenger+ All in One Messenger for iPhone: Covers Yahoo Messenger, GTalk, Microsoft Live Messenger, ICQ and many more.
Pownce: The goodold Microblogging/Social networking service which reaches your iPhone to come to your fingertips.
SnapMyLife - lets you share and view photos, location and mapping features, instant access to your friends’ photos, favorites and comments.
I am not linking these to the App Store so just forgive me and take the strain to type the app name in the App store and enjoy the fun of Social networking.