RealMedia Variable Bitrate (RMVB) is a variable bitrate extension of the RealMedia multimedia container format developed by RealNetworks. It is very popular on the internet, but you can't put it on your iPhone 4 directly. You need to convert RMVB to MP4 format that supported by iPhone 4 first.
To convert RMVB video to iPhone 4, you need a Video to iPhone 4 Converter. Most iPhone 4 Video Converter can help you converting RMVB to iPhone 4 MP4. We recommend you the excellent Cucusoft iPhone 4 Converter Suite! Cucusoft iPhone 4 Video Converter can help you to convert almost all formats of video files (AVI, MPG, MPEG, ASF, WMV, MOV, 3GP, AMR, FLV, FLIC, SWF, RM, RMVB etc.) into iPhone 4 format.
This Page is especially designed for iPhone 4 users who want to convert RMVB to iPhone 4. Follow the guide step by step, you will find it very easy to handle how to convert high quality RMVB movie to iPhone 4.
Step 1: Launch Cucusoft iPhone Video Converter
Download Cucusoft iPhone 4 Converter Suite and run it. You will see the screenshot as the following. Launch iPhone 4 Video Converter.

Step 2: Click 'Open file' button to load the RMVB file(s) you'd like to convert. The iPhone 4 Video Converter software supports batch conversion mode.
Step 3: The default output format is iPhone 480*320 Mpeg-4 video. If you'd like to change this, click "Profile" button, set the output format to iPhone 480*320 mpeg4 video, iPhone MP4 video, iPhone h264 video or iPhone audio (MP3). Here, you can also set video size, frame rate and more.
Step 4: Hit 'Convert' button to start converting RMVB to iPhone 4.

Step 5: Transfer the converted video or audio files to iTunes library and sync them to iPhone 4.
The limitation in the Cucusoft iPhone 4 Converter Suite trial version is that there is a watermark on the output video. Otherwise, the functionality is exactly the same in the trial version and full version.
Related Link: MOV to iPhone 4