I received my One a few days ago, went through hell and back to unlock the bootloader after I already set everything up the way I like it, rooted the phone and updated to XNPH33R and everything was a beauty until I noticed my network acting up. At first it was just the internet connection would drop every now and then then the voice calls started dropping more randomly. I must've flashed my phone like 10 times just to make sure I covered everything.
Then I decided to check the bands used by my service provider, found them on a link on the GSMArena website.
After that it was a matter of setting that on my phone, so I searched online and got this code, *#*#4636#*#*, which should take you to the service menu, there you should be able to make a selection as to which band you want your phone to operate on, as well as the connection type. I set mine to my countrys' band and the connection type to WCDMA/LTE, after that my connection was H+ and it didn't drop for 24 hours now, not even once.
Please let me know if you face any problems doing this. I AM NOT RESPONSIBLE FOR ANY PROBLEMS YOU CAUSE DOING THIS - DO IT AT YOUR OWN RISK.
Oh and the oneplus one is a piece of art, literally.