Of course bandwidth != subnet mask. He should give them whatever IP's they demonstrate a need for in the next three months. Determining and justifying that need has nothing to do with how over (or under) subscribed their bandwidth is.
Let us not forget what some salespersons will promise to potential large bandwidth customers. An OC-3 POS customer, for example, can expect many many /24s. One may say "They should go to ARIN", but alas, they would have to pay another $2500 on top of the $1 million+ they are paying for transit. <8{} It is surprising how much a salesperson will "sell" to get the commission on a 5 year OC-3 contract, forget about OC-12/48... So, in some cases, like it or not, bandwidth sold is proportional to IP addresses. chris
If they are in fact only selling dialup (not leased lines, not web hosting), you might ask how many pops(locations) they plan to have right away, modems/pop, space reserved for internal devices (email/corporate lan) and links. You could easially justify a couple of /24's with a couple locations and IP's for all the new PC's in the marketing dept.
KL