Ok, first and foremost, I will have to say that the easiest way to add wallpapers to your phone is to have a MicroSD card for your phone. To add pictures via the MicroSD card do the following(there are probably different ways to do this but this is the way I do it)
1. Find the image you want on your computer.
2. Plug your card into your computer.
3. Open your MicroSD folders, You should have a My_Pix folder, open it.
4. Drag and Drop the image you want in the folder.
5. Plug the MicroSD card back into the phone and your picture will be there.
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If you don't have a microSD card you can also add wallpapers to your phone through a program called BitPim.
1. Download the latest version of BitPim (
http://www.bitpim.org/)
2. once that is installed on your computer. Open BitPim and your screen should look similar to this.
You may not be able to see the tab that says filesystem so to fix this simply go to VIEW and then View Filesystem and that should take care of that.3. If BitPim doesn't detect your phone automatically, go to to the top and go to edit-settings and where it says Phone Type and then you have the scroll down list. Choose the Touch, Dare, or Voyager settings.

Press Ok after you are done using the dare settings. and now you will be able to see a folder. that opens your filesystem. click the arrow by the folder to open it. *it will probably take a few seconds to open*

The you are going to scroll down to BREW-MOD-1088
Now you should be able to see all your pictures, From here just drag and drop and jpg image and then it will show on your phone.
Hope this helps.