[Voronwe]

I think it very unlikely that Gandalf was refering to his ring when he used the word 'Secret Fire'. As has already been pointed out, Ganalf would not have been a servant of his own ring.

The Secret Fire (also called the Imperishable Flame) is (according to HoME I think) the 'creative activity' of Eru Iluvatar. It seems to be the part of Eru that gives reality to what he creates - thus Melkor's desire to find it in the void, since he wanted to create things of his own. So Gandalf statement that he is a servant of this fire would mean that he is a servant of Eru.

The Flame of Anor could possibly refer to Gandalf's Ring, but I think not. Gandalf kept his ring so secret that I don't think he would ever have refered to it even like this.

-Voronwe