Wow much money would a modern day smartphone be worth in the year 1990? ?

nothing because in 1990 there was no internet or  2G or 3G or 4G or 5G networks 

The phone would be useless for communication. The trend then was analog. Digital carriers were still years away so no calls, no text messages.

The camera may work but where would you get more SD cards? There were none yet. Worse, apart from the phone, where would you view the picture. The best monitors then were just VGA.

MP3? Nah. Four more years before that.

Apps? Hahaha! Even Napster and Friendster weren't born yet. Heck, even Netscape wasn't available yet. The internet may have already been established but the World Wide Web as we know it was just literally coming out. 

So yes, it's a brick way back in 1990.

$0. It would as good as a brick.

You'd get nothing. The service wouldn't be available and the phone wouldn't even work. 

In the mid 80s , you could get a brick phone for 

about £3500. By 1992, you could get a phone recognisable to today’s user ( but just a phone) for about £30 pm, so not really much more than today.

Bill Gates would probably mortgage microsoft for it.

it would be worth alot , the 90's camera in phones where nonexistant , after all the didnt require a camera back then , so much for so called smart phones ..

What you'd get is being disappeared and interrogated by the government for being a time traveller. Think too of all the mistakes and disasters they could avoid if you told them how history had played out.

It would be worthless as a phone and no internet connection would be available.  

You have a camera and a media player and whatever apps were on the phone.  

the support tech so it would operate wouldnt exist lol ... im sure the govt would arrest you and dissect you to see what they find though lol .... back in 90 they knew about the tech and were developing what you use today .. they did have some of it available like say SSD drives .. you could pick you up a 100MB one for probably 5 grand thereabouts ..