No, Iphone does not have BBM but it does have some other apps that can be used for free messaging like text free etc.
Free text messaging apps are available in the Apple App Store for IOS devices such as the Iphone and Ipod Touch. For Android phones, these can be found in the Android Market.
basically picture messaging
There's an iMessage feature, with which you may send free "text messages" (I prefer to call this type of communication "instant messaging") to anyone else with an iPhone 4S. In terms of text messaging, however, as in through your cellular network, I'm afraid it'll always cost something. Unless your plan includes free texts.
It is a plan like any other service provider. AT&T charges roughly $10-$20 for text messaging.
Yes, you can message people and with an ipod you can
it is like a chatroom message
Text Messaging,call,play games etc..
MMS (picture, sound and video messaging) is currently (March 2008) unsupported on the iPhone, although the capability is there and could (in theory) be introduced in a later software upgrade.
In order to do SMS messaging, you will need to first own a phone that is capable of doing it. The iPhone is capable, as is other phones such as the BlackBerry.
I think you can only have a signature on the email.
AT&T does not offer the iPhone 4S without a monthly plan. There are pay as you go options for text messaging starting for 10 cents a text. However, the iPhone 4S has iMessaging which does not count towards text messaging.