I'm new to this and I apologise if this type of question is already on the message board somewhere.  When do you ask the provider for a particular type of service?  In my case, I'm looking for a FJ, do I mention it on an initial phone call or e-mail or should I wait till our app't?

You are paying for a lady's time.  No mention of any sexual activity should be made until the donation has been placed on the table/nightstand and the action begins; maybe while you are beginning to undress each other.

FJ?

I'm not sure what you are asking.  You should probably read the Newbie manual (link at the top of this board).
However you should not discuss any preferances until you are between the sheets.  But if the lady does not have your request on her menu, you may be disappointed.  
You should check her web-site to see if she even offers what you are interested in.  It would also help to read her full reviews, which you should anyway.  Yes, you need VIP to read the full reviews.  The cost is way less than even one spoiled date.  
skb

but they are a very rare occurence so you'll not likely find a review that mentions it; but you can certainly ask once you are in the room and the festivities have begun.

One hint:  If the gal has a lot of prominent photos of her feet on her site, that is a good sign.  (Though not a guarantee.)

if you tell a lady you are really into feet and love to have feet massaging your body, she will get the hint.  you wouldn't have to come right out and ask her about a Fj.

As Mr Fisher suggested look for websites with feet pictures.  Or when in doubt ask the lady you are contacting if she has an foot pics for you to see.

OK, this is not a normal menu item.  I think I'd make an exception and at least give a hint before meeting...  yeah, something like "I'm into feet".  That is not a discussion of a sex act per say.  See what the response is.
skb

You can also post in your local board if any girls are into foot play. I'm into feet and is very hard to find a girl who really enjoys it.