The storm is cdma with gsm roaming capabilities. It might be a ***** to do but it may be possible.
however Alltel does not have a SIM card (since they are CDMA) to put into an unlocked Storm. AFAIK Alltel will not activate it either regardless of it being CDMA as well.
I bought a Storm and I have my phone working on the Alltel network, the only problem I am having is it is not staying in 3G when using the browser but the browser does work , everything else works fine! Phone, SMS,MMS,and BIS! If anyone knows how to get my 3G to workk all the time it would be GREAT!! Oh Visual Voicemail does not work or VZ Navigator, but google maps uses GPS just fine!!
There is a thread for this already, search "storm working on alltel" its your first result. It's posted by jmotl. I'll be using his tutorial as soon as my storm gets here!