If we're talking a large company, your best bet is to obtain the phone number of a business development manager or marketing official via Jigsaw.com.
I would argue you have a bit more leverage in the upwards direction when citing a price over the phone than when stating it via e-mail. In communicating with your voice, have more emotive tools at your disposal to win your customer over and to build trust with him/her and you do with words only. In practice, however, I would probably quote the same price when communicating via either medium.
I will refrain from giving any further cold-calling advice here as I do not consider myself an expert in that area. I would, however, generally suggest you exercise good conversational skills such as careful listening. In most (but not all) cases, lean more towards responding to the customer's specific concerns and making him/her feel comfortable doing business with you than spitting out a pitch verbatim.
If you would like to gain some no-frills professional cold-calling advice for selling domains, here's an idea: pick an expensive name at BuyDomains.com -- ideally one you have at least mild interest in -- inquire about its price over the phone, play hardball with the sales rep ("You registered this for $8 and you're selling this for $6000???"), and note which arguments they state for purchasing the domain you find compelling and which you don't. Rinse and repeat for a different domain name / salesman. Nothing beats a little real-world role-playing!
Federer, Rob Sequin, Bruce Marler, etc. could probably offer much more sound advice regarding cold calling as, unlike me, they are natural businessmen. Many domaining professionals have expressed to me they've found cold-calling to be more time-consuming than it's worth though.
