Perhaps a method used exclusively by very large companies is that way for a reason? Of course purchasing by talking to someone on the phone is extremely difficult. The only reason people sell that way is to make sure they can hassle you as much as possible during the sale.
Apropos of nothing: customers often have an exaggerated notion on how important it is to e.g. an enterprise software company that that company land their account.
A conversation I've had a few times:
"We need it to do $THING_IT_WON'T_DO."
"In that case, it probably isn't a great fit for your needs."
"You don't understand. I won't buy it if it doesn't do that."
"I think I do understand. That's fine. You might consider trying $COMPETITOR, although you should know their minimum spend is $1,000 a month."
"That's outrageous. You have a $29 plan."
"Yes. So you should go with the competitor if that requirement is worth $971 a month to you."
"No, I want to spend $29, but I absolutely need that."
"I understand where you're coming from, but we do not offer that feature, and if we did, we would charge prices close to what our competitor does for it."
"You're not working with me here."
"I'm trying to find a resolution which works for you, but including that feature at $29 doesn't make business sense for me, so I won't do it."
"Put me on the phone with your boss."
"I'm afraid that isn't possible, as I sort of run things around here."
"What sort of businessman turns customers away."
"You're not a customer. If you were, you would be purchasing a product I sell for the amount I sell it for. That isn't happening. That's fine. Have a nice day."
That's fine. 'patio11 has lots of stories about that.
However, the lack of up-front pricing data isn't being used to justify "I won't do business with you." It's justifying "I'm going to take all your stuff anyway."