For me, the status of the person with the cel as 
either a "dealer" or a "friend" would make a 
*big* difference to what I did. If the person 
were a dealer and I were making an offer on the 
cel, I wouldn't write if I didn't have the cash 
already in hand. BUT. . . If the person were a 
friend, and I wanted to offer on the cel, I would 
most likely add on to the end of the offer e-mail 
that if they accepted, I planned to sell cels X, 
Y, and Z to come up with the funds.

On the other hand, there's a third option here. 
That is, having someone lined up who would be 
willing to temporarily *loan* you the money while 
you sold the other cels if your make your offer 
is accepted. That way you can (in a way) both 
have the money on hand, but also not lose out 
completely if your offer is not accepted.

Or there's the fourth option of hoping the person 
who you're talking about replies to this thread 
and states what their own preference would be. ^_~
Good luck. ^_^

Many Sharp Smiles,
--Drac