Elon's tweet also doesn't mention upload speed. Download speed isn't very useful when your trying to send a MMS showing where your trapped and it's taking tens of minutes to upload.
> Note: Your coordinates and elevation may not be available in certain countries or regions.
https://support.apple.com/en-gb/guide/iphone/iph1ac0b663/ios
Article opens iPhones of several generations since iPhone 3G to discover how they do GNSS positioning.
You also need to be able to get a session within the beam. If you're stuck in the middle of a desert you'll be fine, but if you're within range of a minor town you may not be able to get any signal.
>@Elon: This service works in partnership with wireless providers, like what @SpaceX and @TMobile announced.
In your scenario you would likely be sending text/sms based communication as a primary priority (ie. coordinates, instructions) with MMS as a secondary luxury.
If you are permanently or frequently in an area without telco service you would want to make use of specialized hardware which is optimized for starlink communication. For example, here is video of Elon using starlink for video conferencing which demonstrates not only high upload speeds, but also quick swapping between satellites without disconnect.
So it really doesn't say anything about upload speed.
Imagine you focus a high gain antenna dish A at an isotropic antenna B. A will almost exclusively hear B, but B will hear things from all directions, making it harder to single out A. Now, A could use their higher gain to scream louder at B - but that's not always a viable option, and could just peak the frontend of B if done wrong.
Different antennas and radio circuits have different selectivity, dictating how they react to nearby noise. A dedicated tranceiver station is often much more selective than consumer devices meant to handle many bands and protocols using a small set of multi-purpose antennas and with space requirements limiting room for radio frontends and filters.
The power rating of a dedicated transceiver station may also be quite a bit higher than that of a portable device, adding to the asymmetry.
There are also differences in atmospheric effects - primarily reflection and refraction - which for these wavelengths happen in the troposphere. With refraction happening closer to the ground (from the perspective of orbit), that makes for another SNR asymmetry.