I’ve just done a little flight, to FL064, comparing the two apps. I used WA to talk to Achim and used TG to get the wx data from his site.
Both apps work similarly. They were fairly usable to about 4000ft over central Sussex, becoming almost useless over Kent (as previous tests showed, Kent doesn’t really “work”).
Finally, some requests were queued up at around 5000ft and didn’t get sent (over Kent) and then I flew back and landed. Curiously, none of them got sent even after landing. They got sent some minutes later.
Of course this test was just Sussex/Kent, UK, and with a specific phone (Samsung S6) and a specific network (Vodafone UK contract).
The conclusion I think one can safely make is that neither app actively checks the connectivity (whatever “connectivity” means) except relatively infrequently, say every few minutes. They certainly don’t do it every few seconds or so, which IMHO is what is needed to grab a very brief bit of signal at high altitudes.
So if Pilot A reports that it works at FL200, it could be because
I did more testing today, on a trip from Zell am See LOWZ to Shoreham EGKA, and also on the way to LOWZ 2 days before (though on that leg the wx was not in question).
I got very sporadic connectivity at FL090-110. Probably once per hour.
So I think my earlier view
The conclusion I think one can safely make is that neither app actively checks the connectivity (whatever “connectivity” means) except relatively infrequently, say every few minutes. They certainly don’t do it every few seconds or so, which IMHO is what is needed to grab a very brief bit of signal at high altitudes.
remains. Some messages did not get sent until a minute or two after landing.
The behaviour of this stuff might be heavily dependent on the particular phone’s telephony stack (the software which interacts with the cellular network). I am sure that there are plenty of bugs in this in many modern phones. The old ones e.g. the Nokias of 10 years ago used to be much more reliable, but then we did not have esoteric stuff like voice and transparent routing of voice and SMS over 3G or 4G which I reckon is responsible for many connectivity problems especially in marginal signal situations.
The level of functionality is probably good enough to avoid the need for a satellite phone, for the “low level” flights like FL100 or below. OTOH you absolutely cannot rely on it.
Today I found that conventional SMS got through better than Whatsapp, which is contrary to what one would expect, but the reason is probably less than obvious: modern phones permanently abandon retries on a particular SMS message after a few tries (hacked phone firmware is a way around this stupid problem) whereas the messaging apps will always eventually get through once internet connectivity is restored.
Tested today at 4000’. No luck, loaded thumbnail image but not full image (I think). Interesting, the requested loaded on both my iPhone and iPad so I guess that improves the chances of an update, especially if with different networks. It is an amazing preflight service to download different products quickly!
It is very obviously heavily (but not totally) dependent on 4G (“LTE”).
When I see “LTE” pop up on the phone status bar, sure enough I get every pending message sent and any pending returns received, in a second or two.
And if the signal lasts say 10 seconds, I can grab the last 100 EuroGA posts 
3G (HSPA or whatever flavour) delivers a pretty good raw data rate but is never anywhere near that good for making use of the signal the moment it appears.
Unfortunately 4G is hardly universally available.
The Telegram based wx delivery service is indeed brilliant, even for ground use. It is much faster than any website.
I tested this today but I can hardly call that an altitude at somewhere around 900 feet. My first scud running flavored flight, too. But it was handy to receive an updated radar image and the destination METAR. I was mostly on “Edge” (pun intended) and received the radar image within a couple of minutes and the METAR within a couple of seconds.
UMTS is 3G and LTE is 4G.
4G can be very different on range depending on frequencies used. 2-3km for the 2600MHz and up to 20 for the 800MHz frequencies.
O2 would be the best network in UK for LTE in flight.
Apologies – I meant LTE, not UMTS. I have edited my post.
My S6 phone doesn’t seem to ever indicate “UMTS”. I see “3” or “H” or “H+”.
Very interesting info, @mdoerr. The problem with O2 is that their roaming data options are (or were till very recently) rather useless.
What is needed is a flight test with an O2 SIM card
mdoerr wrote:
O2 would be the best network in UK for LTE in flight.
I’m not sure you want longest range for this application. Longest range also means most cochannel interference.
I had LTE connectivity in FL160 near Aachen, that was in the 800MHz band.
How could it work with a 2,6GHz tower if the range is just 3km and I’m more than 5km above?
You need the range!
For true anoraks only: there is a subtle difference in the way these two apps tell the sender that your message has reached the recipient.
Whatsapp shows 1st tick when it has left your phone and the 2nd tick when it has reached the message database of the app on the recipient phone. It doesn’t say anything about having been seen. This is similar to standard SMS with message delivery confirmation enabled.
Telegram shows 1st tick when it has been delivered to the recipient phone, and the 2nd tick then the message is displayed in the app message window and the window is actually visible to the user, so if e.g. the app is on top but you have the screensaver on, the 2nd tick will appear only when the user has swiped away the screen saver. This is a really clever implementation which is exactly what you want for “normal life” where you need to know if the message has been read. It won’t be popular with people with, ahem, “unusual psychological needs” who want to receive and see messages without the sender knowing they have seen them 
because the next best thing would be the recipient app returning a photo of the face of the person reading the message!
There is also a difference in the behaviour of the PC version of the respective app. I have not tried the Whatsapp one but apparently the messages go to the phone first and the phone sends them on to the PC app, so if the phone is offline, the PC app doesn’t work. Telegram works much better in that the messages get delivered to both the phone and the PC app concurrently and if one is offline the other gets it anyway, and the system implements a superb sync scheme whereby if e.g. you delete a message from one app it instantly vanishes from the other one too.
Both apps have an obvious privacy issue in that if somebody gets hold of your phone for a minute or two (needed to register the PC version of the app) they can get real time copies of all your messages on their PC, anywhere in the world But unauthorised physical access is the end of all information security anyway… and anyway this has always been possible with SMS etc etc.
I did more tests with these apps over Belgium, Germany and Austria on 10-12 July. As previously, they do work when there is internet connectivity for some time. With 3G/HSPA you need maybe 10 seconds of connectivity. With LTE you need only a few seconds and Achim’s Telegram wx delivery service will get you a complete weather chart in that time. But you can go for an hour or two without any connectivity and this is FL100 over Germany… It does nevertheless move the need for a satellite phone quite a long way back for many people.
