Sony had things like the clie, and microsoft had any number things running Windows CE (with internet browsing since 1996, though PocketIE was not the best and 2002 would be internet explorer ce before something vaguely competitive happened), HP had long had palmtops with serial ports and options to get a modem going on, touchscreens were nothing new either. The idea that someone would bolt on a mobile phone transmitter to a PDA would not have been terribly alien.I
I thought you were talking about if we had to take a current technology and revert it to its primitive form.
It would not be so many years before various European phone companies (Americans generally got laughed at for their horribly primitive phones, and I don't think even Japan knows what happened in Japanese phones during this timeframe, Japan did have some interesting stuff a few years later too though) came along with a somewhat programmable phone either (and pocketPCs were long since quite programmable, probably even more open than phones today). Blackberry had java running phones capable of email in 2002, and more pager type things earlier still, see also Symbian for one time super popular OS in such a space. First phone virus (cabir if you want to look it up) was 2004. Maps on GPS enabled phones was a bit later affair (Nokia N95 probably being my first interaction and that was 2007 or so I think, https://pdroms.de/nintendo-nintendods-nds-ds/treasures-of-gaia-v0-2-nds-application having google maps/satellite view also in 2007 on the DS) but GPS devices were common enough to be mundane.
The idea of making it as "open" as the likes of apple and then android was seemingly a bridge too far for the makers of such devices* and they tried to lock them down hard, charged outrageous access fees and whatever else but you could have paid your money and programmed something nice, with several companies having rather noted custom setups.
*possibly also the FCC (see history of software defined radio and the FCC) but I am speculating at that point.
Basically dropping things back 20 years on phones would not change an awful lot depending upon where you are in the world, and if it did it would only be for a year or two. Now I am operating under the idea that people were using phones as a phone that maybe had some other communication forms rather than what it is like today and that might be radically different unless you were a businessman or a super turbo rich nerd (in which case you might just able to pull off an effective equivalent).