hm, i usually pronounced it like "Tecke - leelee". But i think i just do so because i have heard it often pronounced this way in the great Song "Horror of Antarctica" from one of my favorite Bands called "The Vision Bleak"
If i remember right, there is a section in one of my old Cthulhu RPG books, where the writers included some information on pronouncing Mythos phrases. I will take a look when i am back from work.