> After you input the [cellphone number], is says its not a valid
> number, but his iPhone can still call his VM.
>
> Any clues?

Try putting his SIM in another phone and see if there is a VM dialin
number in SIM phonebook; it should be in the first entry. The reason I
say this is because my wife's iPhone "died" once, and I put her SIM in
another phone while I dried out the water in her iPhone <g>. And she
could access VM through the standard hold-down-1 method despite it
being an iPhone account. It wasn't a leftover number in the phone
memory either, because it was an unlocked T-Mobile handset. Must have
been a SIM phonebook entry.