Just follow step by step instructions below, you will find it is really easy and handy!
Step1. Launch Cucusoft iPhone Video Converter
Open the software, you will see the screenshot as the following. You can download the trial version free , also you can buy the full version, $29.95.



Step2. Click 'Open file' button to load the FLV file(s) you'd like to convert. The iPhone converter software supports batch conversion mode.



Step3. 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, iPod MP4 video, iPod h264 video or iPhone audio (MP3). Here, you can also set video size, frame rate and more.

Step4. Hit 'Convert' button to start converting FLV to iPhone.

Step5. Transfer the converted video or audio files to iTunes library and sync them to iPhone.

Video to iPhone

1. Click “Video to iPhone Converter” to load the Aimersoft Video to iPhone Converter. Then click “Add” button to load video files. This software supports batch conversion, so you can add several video clips at one time.

2. The operation is similar with DVD to iPhone Converter, this software can join several different video clips into one file, if you want to join video, just check the box “Merge into one file”. You also can customize the resolution, video bit rate, encoder, frame rate, audio bit rate, channel, etc in the setting panel by clicking the “Settings” button. The program also lets you create a profile and save it, then you can use different settings for each video clips.

3. Click “Start” button to start the conversion after you finish the settings.
Tips:
1. This software provides rich video editing functions for you to trim, crop and edit DVD movie. If you want to crop the DVD movie, just click the “Crop” button, and then you will see a pop up window (See the figure below). There is a frame in dashed line around the movie video; you can drag it to cut the black edges. More over, you can click the Crop drop-down list to select a Crop model you prefer, for example: “Cut off top and bottom black edges”. You can even type the number in the box to cut off black border accurately.

2. You can click the “Effect” button and customize the brightness, saturation, contrast, volume, etc (See the figure below). You can even apply special effects such as “Emboss”, “Negative”, “Old film” and “Gray” by selecting an effect from drop-down list.

3. This software can capture pictures from DVD movie, there is a small camera icon below the preview windows, click it when you preview the movie, it can save picture as JPEG and BMP.
Video to iPhone

For mac user,
use this free online converter.
Zamzar - Free online file conversion
But it can not convert big files and it does not support batch conversion. It can not join files to one file.
You can use this video converter. It can convert several files at one time to one file.