This is a much better IM compared to Ping! or even Whatsapp with lot’s of goodies such as group chat, free photo sending, push notification, email as identification instead of coded ID, no need to login and is extremely fast!
Pros

1. Free iPhone to iPhone SMS style texting
2. Group chats
3. PHOTO messaging
4. Read receipts.!
5. Push Notification

Cons

1. Frequent crashing after exiting group chat
2. Plus button & Green Button overlay covers the message slightly
3. User Interface not theme-able yet

WhatsApp is a direct iPhone-2-iPhone messenger chat application. WhatsApp allows you to carry on a conversation in real time with your contacts without having to pay for SMS.

In addition to chat there is a “Status” feature, thanks to which you and your friends will always know what’s up and how to best get in touch.

And with iPhone Push Notifications, WhatsApp can even let you know when your contact’s status changes and what they are up to.

WhatsApp only works among users who have the application, so after you download WhatsApp, make sure to use the “Tell a Friend” feature to share this App with the friends and contacts in your address book.

WhatsApp on iPhone now supports Facebook Connect. Share your mobile status with your Facebook friends and Address Book contacts!

Pros

• Able to use Status functionality of WhatsApp to inform your contacts about your mobile availability
• WhatsApp automatically works with your existing iPhone Contacts. There is no hassle of adding friends, creating accounts, or memorizing PINs and login names.
• No sign up is necessary! Simply download WhatsApp to your iPhone or BlackBerry device and it will automatically work. (Anyone can test this out? iPhone to BlackBerry)
• Super fast text sending user interface with fantastic wallpaper customization support!

Cons

• WhatsApp do not support iPod Touch devices due to their limited network functionality.
• WhatsApp is currently not supported in Malaysia, India, Indonesia, and Thailand.
• Not able to use this app as social networking tool as it’s hard to give mobile numbers to strangers as you can’t block SMS advertising Spam from overseas.

WhatsApp Inc Web Site
WhatsApp Messenger Support

Ping! is a instant messaging client for the iPhone that looks and feels like the built in iPhone SMS client. It aims to provide free iPhone to iPhone (and iPod touch on wifi) messaging with push notifications!

Stop dealing with IM system that log you in and out. Forget about paying your carrier for text messaging.

Once you’ve download the (currently free) app and selected a username, you can invite/find friends and family you know own an iPhone or iPod touch, and you’re ready to go.

Note: Currently you cannot change your username after that so choose carefully!

Ping! is the simplest way to message your friends with an iPhone/iPod Touch. It uses a unique Ping! ID and sends messages for FREE! But wait, what about your friends who have an iPhone but live in another country? No problem, Ping! messages will reach ALL iPhones and iPod Touches AROUND THE WORLD (ANY country!), for FREE!

Pros:

• NO MONTHLY COST. Why pay for data and SMS bundles from your carrier?
• NO ROAMING CHARGES. Some apps offer free SMS but are exclusive to the U.S. or support few other carriers. Ping! is always free, even when messaging overseas and works in ANY COUNTRY in the world.
• FASTER DELIVERY. Messages are not limited by your carrier’s traffic. Notification are delivered in an instant.
• WORKS WITH IPOD TOUCH. SMS only works with phones. Ping! works with iPhone, the iPod Touch, and other devices that Apple may offer in the future.
• NO NEED TO LOG IN/OUT. Why deal with the confusion of getting bumped off wen you log in on another device? Your messages arrive in one place. Ping! keeps you connected at all times.
• NO NEED TO ADD FRIENDS and deal with the tedious process of accepting invitations. All you need is your friend’s Ping! ID to start messaging IMMEDIATELY.
• OFFLINE MESSAGES GUARANTEED. Some IM apps do not support offline messages or only support it with specific software (e.g. MSN). All Ping! messages are stored offline until received.

Cons:

• Unable to change usernames means once you had settled with a username there are no option to switch usernames or add another account, there can be only one.
• Landscape mode got a small bug that removes the text input box but not a serious flaw which developer will fix it up in the next updates
• No way to block spams from unknown spammers, this mean possibility of mass advertising companies acquiring millions of user ID and automatic spam people with advertisements daily (Seriously a possibility that must not be ignored so developer think of a fix if possible maybe a small Captcha before a conversation or something)

Wish List

• Ability to ban or unban by checking the user ID “Edit” option
• Bounced Ping! for messages that contains words set by users such as “<ADS>, You had Won!” and place them in the “Spam” group for user to ban them or remove them from the spam group.
• Send images like MMS.
• Send GPS Map location

Developed by Gary Fung

UPDATE! Now you can submit your Ping! User ID to a International Directory HERE!

I had been seeking the best Tweeter Application for iPhone for sometime and I found it!! Yes, it’s different from Twinkle because it has the support for multiple accounts for tweeter.

I hold 2 accounts due to the fact I use one for personal tweets and the other for this blog for Apple App Review and this application “Tweetie” satisfy my desire to jump from account to account to tweet with targeted audiance.

I had used TwitterFon which is free but it does not support multiple accounts and the tweet nearby functions that “Tweetie” have, the features of this application is simply breathtaking!

Let me list out a few of the “features”

1. Able to search within individual profile
2. Able to check who are the  followers & those following
3. Able to check unlimited the followers of the followers of the followers…and so on
4. Able to Find out what is the latest trends keywords that people are chatting about
5. Able to find out who is twittering NEARBY (But lacks the distance selection that Twinkle has)
6. Able to email tweets that you find interesting 
7. Able to Add Tweets to Instapaper 
8. View Your timeline, replies, direct messages (common)
9. Manage your favorite Tweets
10. Navigate Reply Chains
11. Upload pictures to TwitPic
12. Post link with automatic link shrinking
13. Uses secure Connection (https)
14. Links to StockTwits
15. Optional Landscape keyboard
16. 3 Themes for selection! (Chat Bubbles, Simple, Dark)

This is absolutely wonderful!

View the developer website here

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Whenever I have a moment of free time, I will tweet on my iPhone and chat with nearby people made possible by this wonderful application call “Twinkle”.

Let me list out it’s features

1. Chat with people nearby which you can set from 1Km, 2Km, 5Km, 10Km, 25Km, 50Km, 100Km, 250Km, 500Km, 1000Km to EVERYWHERE!
2. Broadcast what you are up to (much like talk anything and everything)
3. Attach pictures, and web links! (Photos are viewable and links open up in Safari browser)
4. Update your location (Your general location will be updated so that people knows if you are “overseas”
5. Full Twitter Support! Yes, optional opt in to synchronize with twitter.

This application is one of the most useful or should I say “Wicked” of all twitter applications on iPhone other than “Twitterfon”

Twinkle Official Home Page