- Signal quality.
- Phone performance.
- Network throughput.
A "truly unlimited" connection would have you downloading at ∞bps so I suggest both words in "truly unlimited" are slightly incorrect.
I think they mean unmetered.
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I'm getting hammered for "snark" but I'm being serious. If you let impossible phrases like "unlimited" stand in marketing, people get the wrong idea, products are wrongfully sold.
I'm only this angry with T-Mobile because they've had the audacity to stick "truly" in front of it.