Yes you need to have the prepurchase to get access to Demon Summoning. I would provide a link but really have no idea how. Maybe I can threadjack and we can both learn how. Just kidding, kind of.
Bashful Banshee.
Enjoy your day please.
Yes, Issue 17 comes out the 28th April (aka tomorrow).
Dual Pistol and Demon Summoning belongs to Going Rogue expansion. However those two powersets can be played (Demon summoning from tomorrow of) IF and ONLY IF you have done the Prepurchase of Going Rogue.
If you have not, you cannot create a Demon summoner tomorrow (or until you have Prepurchased Going Rogue... or waited until Going Rogue launches then bought it).
Here is a little link to the wiki page (cohtitan wiki.. not that.. bad link): http://wiki.cohtitan.com/wiki/Issue_17
edit: Oh.. a little question on how to provide a link. Here you go.
1. Find the link you want to use. Ctrl+c it.
2. When you do post, you might see some small symbols above the screen (like I would have seen as I now type). You can see various format properties.. amongst them there is a little button that provides an URL.
3. Click that button. You will now get the option of typing in a link, Paste in that link (ctrl+v)
4. Press Enter and woosh.. You see the link appearing in this writing place. You will notice that its doubled up and half of it is marked. What is marked is the name of the link. If I f.ex wanted the above link to say "Click me" I would simply have removed the text "http://wiki.cohtitan.com/wiki/Issue_17" and replaced it with "Click me". Then it would be seen like this:
Click Me
Lady Arete on Unionhandbook
My Excel Badge tool
Thank you to you both for the answers.
Lady a big THANK YOU for goin the extra mile for me. 
Sorry don't have time to search (new job,hooray!) and haven't been playing in half a month.But does I17 come out tomorrow(?),to access demon summoning do you have to do the pre-purchase?
Any answers and/or links are appreciated,I'll check back after lunch thanx...