There has been numerous attempts over the years by unknown actors to essentially crack TOR by controlling nodes. There have been a few theories about who, but it has been a sustained effort over a period of years that has at times controlled up to an entire quarter of the Tor network, leading many to believe state actors and/or law enforcement are behind these man-in-the-middle attacks.
It would presumably be the same it was essentially just a connection to the ISP so it is the same kinds of attack vectors browsing the wider web (arguably less since you presumably could call from random numbers and/or change ip address easily). The only one big thing I could think or is that since plain old telephone lines (POTS) were often directly interconnected (party lines/multiple phones to one line), someone could more easily pickup/tap the line to eavesdrop compared to broadband. USB modems do exist I believe 56k is the fastest you can find (iirc there was some FCC regulation limiting to 53k to prevent telco issues going faster, I believe 56-64k was the technical limit), but if you have a 2G phone that supports Circuit Switch Data you can use that and try out the magic of WML cards (specially formated html pages to run on phones) making up a WML deck / WAP site (mobile version of the site). There is a list of WAP sites here that may still work http://pubquizhelp.com/mobile/bestwap.html
I forgot the details but the 2005 Most Wanted has an unofficial update pack that brings widescreen and other creature comforts. It was well supported except I could never get lan-play to work on my Win10 hosts. I wish I had a link but everything I find is piecemeal and the patch I had years ago combined the popular ones to one patch.