The little tool sendrawpdu, based on iphone-elite's sendmodem is now on github.With an iPhone 4, and this sample code, you can verify my statements for free ;-) .
By the way, I read some comments around saying that SMS spoofing is not new, that one can modify the origin address of a SMS in the protocol and such.
Now tell me, how can you do this without paying a dedicated service which is in fact a gateway talking to the carrier at a lower layer than the PDU data ?
In a SMS-SUBMIT message, you can't change the origin address. Check the specification.