Android - "Converting to multimedia message" when forwarding large SMS

This was fixed in Froyo. Anything over 3*160 (480 characters) will convert to an MMS prior to Froyo.

You do have a couple options.

• Use a 3rd Party Messaging App, like Handcent, for example.
• See if you are able to install this "Hack"
• Root your phone and flash a Froyo Rom
• Wait for a Froyo update from Samsung

Edit: Some additional information
Anything over 160 characters, technically, is no longer an SMS. The stock Messaging app, and others too, allow for "longer" messages but it is just splitting up the messages in to 160 characters. In Eclair (Android 2.1) a message will be converted to an MMS after it exceeds 480 characters. At that point, the default Messaging app will no longer split up the messages, instead it just sends it as one MMS. If you are using a 3rd party messaging application and find that you are still being charged the MMS rate, it may be that your carrier is grouping messages that come through "at the same time".

Use Handcent and change the default settings:

1. Settings -> Send message settings
2. Auto-convert to MMS - Uncheck this
3. Split 160 - Set this to one of the Split options (I recommend Split by word & add counter but you may prefer a different one - I don't fully understand the differences between them all).

Rather than using Handcent, which is quite bulky, slow and doesn't really add any new features to the stock SMS application provided by Android, I recommend BigSMS.

It's a free application that provides you with a simple, yet powerful interface that allows you to send unlimited length SMS. It doesn't claim to be big or clever, it is simply a solution to this problem which the developer also appears to have encountered.

I've been using it for a couple of days and it seems to do exactly what it says. Running perfect on Xperia Arc S running 2.3