Your phone voluntarily tags the hotspot data with specific TTL values which carriers use to segment the data. Not all carriers work the same though.

Different applications on a single device can't apply different TTL's? I thought TTL was a pretty basic knob exposed to applications. e.g. A sensor that transmits fresh data every 20 seconds doesn't need stale packets bounding around clogging up the pipes, while a file transfer over an intermittently delayed link might benefit from a higher TTL.

Voluntarily tags specific TTL values much like your home router does. Some providers assign a different IP to hotspot users.

Super easy to spoof too.