As you move from one part of town to the next, your iPhone intelligently moves from one cellular connection to another in an effort to maintain the highest-quality internet connection that it can. Unfortunately, sometimes the iPhone favors slower connections with a higher signal over faster connections with a lower signal, and this can impact performance.
Those who’d like to have more control over their handset’s cellular network selection might take a liking to a newly-released jailbreak tweak dubbed NetworkManager by iOS developer NoisyFlake, as it lets you switch between preferred network type(s) on the fly.