Now my question is how many of the longer range gliders will carry radios / transponders? As someone previously stated gliders will often not paint on radar - are they required to carry radar reflectors?
Good comments on this already. To add, about transponders: Gliders have not carried transponders in significant numbers in the past. With mode S becoming mandatory in the Netherlands, some gliders now have gotten battery powered transponders on-board, but switching them on is a significant drain on the battery. These types of gliders make flights of five hours or more (let's not get started on the diaper issue) so they only switch the transponder on when they're in a TMZ or controlled airspace transit. They will switch them off afterwards.
At least, that was the official policy that was published on the noticeboards of the glider field where I spent a week learning how to glide.
I've never heard of a (presumably passive) "radar reflector" in a glider or any other type of aircraft. I've heard a story once about military target radar being able to pick up seagulls and such, so I guess with that type of radar a glider, particularly if partly made from carbon fibre, would not be hard to pick up. But I would not know about civilian primary radar, and whether yacht-type radar reflectors would make a difference.
"Why do they not call the most appropriate ATC unit for a meaningful service"
As a power pilot, I agree with most posters here that gliders should be on the normal, published frequencies requesting a FIS or RIS instead of their own frequency, even if that takes a bit of figuring out the proper frequencies before starting the flight. Not that different from what power pilots do. But another factor in this debate is that a lot of glider pilots do not have an R/T license and are thus not legally allowed to operate on most VHF frequencies. The glider frequencies mentioned are typically exempted from the requirement of having an R/T license.
To finish, a little anekdote. A few weeks ago I flew from Rotterdam to Berlin Tempelhof. We were warned about glider championships near EDOJ (Luesse) so we avoided that area by at least 10 nm (routing was north of Magdeburg, EDBG, south of Brandenburg if you're interested).
Near EDBG (Burg) I spot a glider far away, same level. I focus and see three more, flying at the same altitude and direction. I make a comment to my brother who was pax sitting beside me "looks like they're flying in formation". As I say this, I spot eight more, and then another dozen or so. As it turns out, apparently the assignment for that day took them from EDOJ to EDBG and since this was a good thermal day but with (relatively) low cloud bottoms, all these gliders were following one another at approx. 3500'. My altitude. Possibly a hundred of them. Directly across my track.
I climbed over them instead of trying to cross the stream same level. But the funny thing was, I was on a FIS from Bremen Info, who warned me of every traffic they could see on their scopes (for practical purposes, it was a RIS). They knew about glider activity in the area of EDOJ (that was NOTAMed, even), but did not know the assignment for that day. And none of these gliders, apparently, had a transponder turned on. So I never got a warning about them from Bremen.
It seems to me, gliders somehow live in a world of their own. They have their own ideas about radio use, transponder use, altimeter use, airspace use, traffic patterns, risk avoidance and acceptance, navigation methods, GPS usage and so forth. I, for once, am very glad to have done a weeks gliding course so I sort of know the way they operate and think. It's been a real eye-opener for me.