Does it matter where I buy a smartphone?

Background: my only cellphones have been provided by my employer, and I have always selected the most basic ones offered. I have recently decided that I would like to purchase an up-to-date smartphone and plan.
Assuming I find the features and cost I am satisfied with, does it matter if I buy from, say, Best Buy, vs. directly from the wireless provider? Or from Amazon, for instance? I am thinking in terms of difficulty getting customer service if needed.