We bought this phone as a replacement to the old Nokia 7.1 my Wife had for 4 years now, and i have the same.This NOKIA X10 is simply great, it is rather big, but all new Phones are big.We did all the Software updates of the case, then even did a Factory Reset to start off with a Clean Firmware before inserting the SIM Card... we have been using T-Mobile for 10 years now on both our Phones.With the SIM inserted, the Phone started working right away, but soon after, we noticed something strange... while my old Nokia 7.1 was solidly connected on 4G, her brand new Nokia X10 kept bouncing from 4G, then 3G then after a while 4G+, then E (basically 2G)... it was a constant bouncing, and she would receive messages from services like Google Chat at intervals, like... No messages for 5-7 minutes, and then all of a sudden, 4 messages come through in rapid succession.Making a Phone Call was difficult, essentially, every time it was jumping networks, between E and 3G and 4G and 5G, the Call would Drop, and that was happening every about 5 minutes.SO WE CONTACTED T-MOBILEthey first of all suggested to disable 5G because we do not live in an area with much 5G coverage yet (really 5G signal gets stopped by anything regardless, so it's better to leave it off anyway unless you're outside ;-) , and that can cause issues with call Drops.then they re-provisioned the connection to her Phone and made us do a Network Reset.IT STARTED WORKING MUCH BETTERThough we found it strange my old Phone would have Full 4G signal while hers only would get 1 or maximum 2 bars.Plus every time she would go out in the back hard, her calls would Drop...Spoke again with T-Mobile, and they said it was because our connection was disconnecting from the Home WiFi and jumping to E instead of 4G, so they suggested to disable the "Voice Over WiFi" as well as "Voice Over LTE" functions so Phone calls would always go through Phone Network instead of Data Network.FINALLY NO MORE DROPPED CALLSBut the Data issue was still there, as we took a Drive, her phone kept bouncing between 4G+ to 3G to 4G to E just about every 3 to 5 minutes, while 5G we kept it disabled regardless.Sending an eMail was a nightmare, only way to achieve so has been to stop in a place where she had good 4G signal.We called T-Mobile again, and this time we got transferred to a "Specialist", whom verified how our Phone communicated since we were less than a mile from a tower.THIS PHONE ONLY PARTIALLY WORKS ON T-MOBILEthese were his exact words.So then he told me how to do some research, and here is what i found out:The T-Mobile 4G Network works on these Frequencies:B2 - 1900MhzB4 - (1700/2100Mhz)B5 - 850MhzB12 - 700MhzB66 - (1700/2100Mhz)B71 - 600MhzFor licensing purposes, every area may be covered under a different frequency.The Tech explained it is something the FCC establishes when they sell Network Maps at auctions... It would be a wish to cover the whole country under one Frequency.THE NOKIA X10 ONLY PICKS UP SOME OF THOSE FREQUENCIESTo be specific The X10 supports only:B2 - 1900MhzB4 - (1700/2100Mhz)B5 - 850MhzAny time the area is not Covered by 4G under one of those Frequencies, the Phone has to skip Network and switch to a different one (3G or E) which can cause call droppings and login issues.WE HAD TO RETURN THE PHONEBut we really liked this Phone, and still wanted to be able to use itWE GOT A NOKIA X20 INSTEADAnd it has been working Perfectly on the T-Mobile Network.So if you have T-Mobile, DO NOT get this X10Get the X20 i stead and will work Perfect.THE NOKIA X20 IS THE SAME PHONE,AND IS FULLY COMPATIBLE TO T-MOBILE NETWORSIf you use something else other than T-Mobile, the X10 will probably be perfect and i can assure you, THIS IS A TRULY GREAT PHONEI would have given it the 5 Stars to this NOKIA X10 if it wasn't for this issue with Network Compatibility... I hope they will update the Amazon Page indicating that it has limitations of T-Mobile NetworkHOPE THIS IS USEFUL