If you are dead set on having wireless Dial-up, I can attempt to guide you but honestly, it isn't really possible. You will end up buying a router you have no use for. As was stated, dial-up routers are obsolete and never really worked well. If you bridge your Dial-Up connection and a wireless adapter setup for ad-hoc, you should "theoretically" get wireless dial-up. The problem is, no wireless router is going to accept the dial-up connection and send it out. That is because it will reject the fact that you are using a phone cable to connect it. You can't do that, it won't work. That's not how telecommunications work.
I am telling you not to buy any wireless equipment unless you intend to upgrade to DSL. A regular, off the shelf router will not work for what you are attempting. It simply isn't a possible function. If you feel the need to try it, do so but, don't expect results. Yes, you will get a wireless notwork. No, you won't have internet unless you bridge your modem and network card. Even still, I have my doubts that it will work. Contact your ISP and consider getting DSL. It will be worth the cost/investment.
Also, the technical information in this post is more to benefit other technically inclined people, those that understand ad-hoc and the complexities of a network. Maybe they can explain it in terms you can relate to but it isn't something I would even ever consider.