Depends what model and who is selling it lol; almost any WinMo 5.0 or above phone (so any post 2003 WinMo phone with wifi) with Wifi on it, can technically act as a wifi router/hostpot, as WinMo has ICS built into it.
It can be a bit of a pain in the arse to setup though, as you need to mess around with the IP setting etc, which is why I suggest opting for a phone with Wifi built into the ROM tbh. However, there are 3rd party apps available, such as WM Wifi Router etc, which essentially take control of ICS and do all the hard work for you.
HTC made a habit of including the feature in ROM's around 2006ish , though most EU network providers (especially UK ones) removed it from their stock-ROM's as it isnt really allowed on their networks.