Telegram wants to give you a subscription to Premium for free. If you enjoy the app, and want to take advantage of additional features like 4GB file uploads, faster download speeds, and premium stickers, that offer might seem enticing. Just know, though, if you accept, you're throwing your privacy and security out the window.
As reported by TechCrunch, Telegram is offering users a free subscription to Premium in exchange for a ridiculous ask: The company wants to use your phone number as a relay for other users trying to log into their app with SMS-based 2FA. According to the terms of the program, you agree to allow Telegram to use your number as a relay for up to 150 OTP (one-time password) SMS messages per month, of which you are responsible for paying. Depending on your region, it's possible this could cost more than Telegram Premium itself. Of course, if you have an unlimited texting plan, it won't cost you anything.
But more troubling is that Telegram acknowledges that the user receiving a OTP SMS-code from your relay may be able to see your phone number, and that the company has no way of preventing this. On top of that, "Telegram will not be liable for any inconvenience, harassment or harm resulting from unwanted, unauthorized or illegal actions undertaken by users who became aware of your phone number through P2PL." Cool.
It seems possible, too, that you'll be able to see recipients' phone numbers as well, as Telegram forbids you from contacting them when using this program, even if they reply to you.
Sure, privacy is dead, and our phone numbers are likely floating around the internet anyway. But why add onto that, especially when you are essentially handing strangers your number? The strangers could potentially use your phone number to send you spam or malware, or mine for more of your personal data online. It just seems like a completely unnecessary exposure of personal information from both sides, just for the privilege of accessing additional Telegram features for free.
Right now, the offer is rolling out to Android users in a limited number of regions, so it isn't a particularly widespread program. However, if you do receive an offer from Telegram, I strongly recommend ignoring it. If you really want Telegram Premium, pay for it with money, not your privacy.