Sorry, Flyhigher, I just saw your reply. I hope you take a read when you get to Asia and can use what I'll give you here.
Here's my take on each city with the caveat that I prefer more gfe and non-pro girls although they are much harder to find...and, yes, I know all girls want something but I make the distinction between hardened pros and the girls more toward the occasional trick end of the spectrum.
BKK: I occasionally hit the Sukhumvit scene but mostly as a voyeur than as a player. I think the best value in all of BKK is Tulip massage parlor which is on Sukhumvit around Ekamai stop on the BTS...ask most guys around Suki and they'll be able to give you the exact location though it's very close to Ekamai BTS station and is right on Sukhumvit.
I always stay in an area called Banglamphu, about a 10-minute walk from Khao San road, backpacker area, and made friends with a couple shop girls who became occasional lovers...for very little money, definitely not players.
The reason I like it is that there's McDonald/s or Starbucks type quality control. I have never been disappointed there and the girls consistently deliver quality, gfe-like experiences, with dfk, bbbj, etc. I have even seen one there a few times who allows me BFS...it's possible...and the personal shower and shower play is incredible. The price at about $75 for the hour, all up, is pretty good too.
I have also had some luck in the Bier Garten on Soi 7 as well. Overall, the quality and service is mediocre at best but you will find the occasional newbie who wants to establish herself.
Phnom Penh: A real hit and miss city, imo. I really don't like the main monger area and bars so prefer to make contact with girls during the day. Amazingly, you will find more English spoken in Cambodia than Thailand so it's not as hard as you'd think to meet girls on the street...lots of province girls come to PP to study, work and look for other opportunities. I love the Cambodians and find them easier to meet than Thais or Viets. Try the National Art Museum, the French Center (somewhat like Alliance Francaise but a different name) with a restaurant and library, or go to markets...you will defintely have a chance to meet girls.
OTOH, if the pro girl community is your thing, there is no shortage in PP....just not my thing so I can't recommend any places.
Saigon: In my experience one of the most frustrating cities in Asia for sex....Quite a few handjob places but they are definitely not service-oriented. The scene is very underground and a lot more tease than pleas in my experience. Having said that, I went to the same restaurant for breakfast for about a month in Bui Vien (backpacker area) and became very friendly with a sweet 27 year-old waitress...we became good friends....and we went out for the last three weeks I was there and she was the most sweet, willing, and hot partner I've had in a long time....and no money exchanged hands...she remains a friend.
Not sure if you will have time, but I recommend using Date in Asia (www.dateinasia.com) and Tagged to try to hook up...I've had some good luck there. Whatever you do, stay far away from Craigslist...crawling with LE...I had a very bad experience that ended up costing me about $900 to buy my way out of the hands of Bangkok's finest law enforcers.
So, hope that helps, my friend....I do note that you won't be visiting the Philippines....truly the jewel in the monger's crown when it comes to beautiful, willing, eager girls....But maybe another day....