make sure you package the VPK with Contagion's VPK exe tool, else it will cause crashes. other than that, changing the phone model should be the same as any other weapon replacement.

I recommend using the QC files from Contagion SDK

i use the crowbar ,the setting is contagion game fgd, made vpk and then put it to addons test, it can load. but restart game, the model can not be load... just first time to load .... unbeliveable, you can download my phone addons test. change vpk file name reload the game it success.... i dont know what is the question............