Gmail introduces sms message

Google which has already taken over a majority of space in the mail communication arena through its gmail, it now seems to enter into the sms communication thereby entering into the mobile communication, even though there are lots of free messaging websites available online, gmail sure has lots of advantages since it provides the flexibility like

1. Messaging right from your gmail account, even when you are editing your mails or checking your inbox
2. It also provides the convenience of your contacts being readily available, also with the android phones backing up your contacts to gmail would make it easier
3. You will not have to type in and log into other free sms providers.
4. You will have the convenience of sms to be viewed in the form of a normal gmail chat and moreover you can check them out later in your chat history.

Now does google provide this all for free, other companies who provide free service depend mainly on ads for their revenue, Google sure would not display ads on your gmail account, currently google does display ads in gmail but its very limited and of smaller size.
Yes it seems like they are charging you in a indirect way, they put a cap on the messages to 50(not daily), but if it turns to zero in a day, it will go back to 1 in 24 hours.
How to renew your message credit ?
It is said that your message credit would increase by 5 (maximum upto 50) every time someone replies to your messages, which means they should reply from the same message you sent them which would reach you on your gmail chat box.
The charges as said currently are the regular charges charged by your service provider.
Messaging is simple just like a chat
you type in the number and start sending sms,

What if the credit goes to zero?

if your credit goes to zero, as already said it would go back to 1 in 24 hours time and you can renew your credit by sending a message to yourself and replying to it as many times you need say replying ten times would restore the credit to 50, and you will be ultimately paying your service provider for those messages.