SPOLIERS AHOY!
The person on the phone is prolly one of the crew of Death Mask Productions, as the Tzimisce clearly states "It wasn't meant to fall into mortal hands"... And would have little to no reason to want to sell such a thing. No doubt this is DM's way of selling the item while retaining anominity to some degree.
The vampire taxi driver, like all sane and intelligent vampires... Which clearly you weren't... Understands that the KoE are vampires from a time when east was east and west was west and never the two should meet. They hate 90% of western culture and 110% of western people and 155% of western Vampires... Seeking only ways to undermind, destory and just generaly hurt them in some manner. The poor guy was prolly trying to hold back peeling laughter as you said to him "No no, please, I'd LOVE to be killed in new and interesting ways by the Asian blood drinkers."... Either that or he had some hope that you'd do something clever with your unlife and instead you chose to spend the better part of it underwater tied to a box... Sure, eventualy you'd get free when you either found enough blood to pump or the things holding you in place decayed away, but by then who cares about you any more? Definatly not the KoE who are in charge.
Because of that all KoE are trying to kill them all the time, and vis versa, no vampire likes the KoE, and thats why they are all against the idea of you sidding with them. It's just plain dumb... And the game rewards you in a fitting way for being dumb. Hopefuly the schools of fish can teach you how to make better life choices from then on.
The character that is the main character in the game never gets mentioned, to the best of my knowladge, in Gehenna. I understand the events in the game get a passing paragraph or something, nothing important.
The term "Methuselahs" is used to suggest any vampire whos lived for a VERY long time. Older then "Elders", "Methuselahs" are equivilent to dirty nuke bombs... You never know what dammage one is doing or when it's going to go off. Most of them sleep the modern age away in secret havens, weary of the world, but those that are active are some of the most powerful creatures to grace the globe.
As for "more information".. There are a couple posts on here talking about White Wolf lore and such, but ultimatly you'd have to go out and get a copy of "Vampire: The Masquerade".. Which is now no longer in print. Try
http://www.white-wolf.com or driverthruRPG where you might still be able to order a copy.. Or hunt down and kill and geek and steal his copy... But not my copy... Um.. Another geek.
Oh, and my lawyer tells me that what I meant when I said "Kill" was "negotiate for purcahse"