The iPhone shows an error when you try to open an Excel file you’ve created in OpenOffice. The exact error is

The document was created with an unsupported version of excel.

Now it may seem at a glance to be unfair. OpenOffice support for MS Office formats is pretty reliable. No desktop OS has trouble with it.

The trick to solving this is in the error message itself. The file was created with an unsupported version of Excel. You’re thinking “nah…”. Yes. Create a blank file in Excel. Open it in OpenOffice. Paste all you want. Save. Ta-da. You now have an iPhone and Blackberry compatible file.

Here’s one in case you need it:
Blank Excel File

Update: This only works for one day. Trying to use it longer with OpenOffice results in the error, too. At this point I’m using ThinkFree Mobile.