For all the things VZW does right, sorting out problems with plans and billing is something that is much too unreliable. Some reps are very good at getting things right and working the system in the customer's favor, and some reps couldn't find their butt if they sat on their hands.
Before calling, make up a written (really - write it out!) list of talking points - what do you want done by the end of the call. Take written notes of what was said - VZW does it ("oh, yes, you called on June 5 about this issue" as all too common a remark), you should, too.
If you think you got one of the clueless reps, try to wrap the call before they do any real damage and call again. The odds of getting the same rep twice are almost zero (I did get the same rep twice only once in all the time I've used cell phones, going back to the days of bag phones). If you still think the wheels are falling off, ask to speak to a supervisor - be polite but insistent.
Finally, never,
ever shout at or threaten a rep. It won't fix a thing. If you think you have one of the ...ah... less skilled reps on the other end, end the call ("this just isn't working for me, I'll call later").
We visit Europe regularly and find the phone landscape changes each time. It's frustrating, annoying, and rarely inexpensive. Life is like that some days - deal with it as best you can.
- - -
SIM's and unlocking... unless you're prepared to spend a lot of time negotiating the European phone markets and dealing with taking your DINC2 out of the expected nets, do nothing except
call VZW before you leave the States.
Call VZW as soon as you return to the States - do it in the airport (but never, ever in the CBP secure zones unless you want to meet customs agents up close and personal). Once you return and have your global stuff turned off, call *22899 to update your roaming info (*22899 is the same as *228 and punching 2 once the call is answered).