Unlocked cell phone & SIM requirements for use in Poland / Europe

I have researched this extensively. From what I can see, I will need is unlocked GSM dual SIM quad core phone. I have a really old GSM phone, but it isn't even a Tri-band, so I don't think it will work. I am also trying to buy a SIM card in advance that will be usable in all four countries (Czech, Austria, Hungary and Poland - in that order), without having to change SIMS every time I go somewhere else. I have found something called Three UK, but it only allows FROM these countries TO UK. I have no reason to call the UK!!

Anyone know much about getting SIMs here in the U.S. first? I'd rather have it ready to go before I get there. I've seen people complaining that once they arrive somewhere and want to buy a phone and/or SIM, they sometimes have to wait a long time in line to get them. Not only that, but they can only get a SIM for that country. I don't want to have to get a new SIM every time I go to a new country.

Thanks for your help. Wouldn't it be wonderful if I could just borrow an international phone. In my dreams!!!

Poland is in the EU like Czech Republic, Austria, and Hungary. Therefore, you can buy a Polish SIM card and be able to roam between these countries as well as other EU countries without roaming charges:

bbc.com/news/business-40281013
This means you can use a single SIM phone instead of a dual SIM one. If you want a Polish number and a Czech, Austrian, or Hungarian number as well, then you can use a dual SIM card.

You need to show your passport or national ID before you can purchase a Polish SIM card. So, I doubt you can just purchase a SIM card online without having to show proof of identity. You do have many options to buy a SIM card when you arrive in Poland, so waiting for long lines is likely an exaggeration.

Regarding your phone, check the supported cellular frequencies in Poland here:
worldtimezone.com/gsm.html
Then, find the technical specifications for your phone and see if your phone supports these frequencies. For GSM voice and text, if your US phone supports GSM, it will work in Poland. For 3G & 4G / LTE data, your US phone may not operate fully if it doesn't support all the Polish cellular provider frequencies. Also, your phone must be unlocked from a US service provider, so you can use it with Poland service providers. If your US service provider supports international roaming (like T-Mobile), then look into it as this may be a better short-term option rather than just buying a Poland SIM card.

I am starting out in Prague so I have to get the SIM either there or here first in the U.S. As for a phone, I managed to buy a slightly used BLU Vivo 5 mini for just $25. It works on all bands. gsmarena.com/blu_vivo_5_mini-8541.php

I found a SIM I could buy in advance and be all set. It is supposed to work in all countries for 30 days. It is listed on Amazon as: PrePaid Europe (UK THREE) sim card 12GB data+3000 minutes+3000 texts for 30 days with FREE ROAMING / USE in 71 destinations including all European countries.

It's only $30. I was told in an answer to a question that I posted on the item that it can actually be activated here in the U.S. before departure. Comments/reviews claim otherwise - that it has to be activated in the UK. I have no way of knowing who's right.

Am I likely to do any better than that by buying a local SIM in Europe??!! (the CZech Republic to begin with) Can I call the United States using a local European SIM? Or can I only call within Europe?

The host of the first place we'll be staying said to buy a prepaid sim card after our arrival, saying that Prague is in the European union as well as Austria, Hungary and Poland so that any sim card I get in Prague will work in the three other countries. But again, if this other SIM works fine and I can get it in advance, and it costs the same or even less, what's the advantage of buying it locally in Europe after I arrive?

a basic SIM card for a pre-paid number here in Poland is in the range of couple of zlotys (PLN) I guess it is similar in the Czech Republic - you can buy it in every news agents (or whatever it is called in American English) - the top-up cards (or rather coupons) for those pre-paids are also ubiquitously available (again all newsagents - newsagents are often in kiosks here) and are relatively cheap

the simplest solution is just buy a pre-paid number in Czech Republic when you are there and then repeat that in Poland - it costs peanuts - as for activation of the number I can't recall to be honest - I have bought mine years ago and I just simply don't remember how it is done - if there are some instructions in Polish (or Czech respectively) ask local people to help you (I wouldn't expect instructions in English for a pre-paid SIM card in Poland to be honest)

If you buy a prepaid number here then you need to get that activated - you will need to go to a shop with your passport and they will register you. It is best to get them to activate it in the shop as well and test that it is working before you leave the shop. Whole process can take maybe half hour as there are often queues.

Not sure which shops do the registration - definitely the cell phone operators own stores which are in pretty much every big mall. possibly also some of the newsagents like in Medio or Kolporter though i know a few of them quit doung that because of the queues/hassle.

sorry to have mislead you Mary - I completely forgot about the recent regulations for pre-paid cards - but well I bought mine years ago and it was straighforward back then

That's okay Gumishu. I managed to get a SIM called Three UK. It has a UK # and can call like 72 countries. It has 3000 minutes, 3000 texts and 12 gig of data good for 30 days. I will activate it a couple days before I leave the U.S. I can also use Google Voice for calls to/from the U.S. because the US Sim does not include the U.S.