I will share this publicly, which isn't something I usually do, because I really had a good experience with these guys.
Had to register a Telegram account about 2 months ago and managed to do that thanks to onlinesim.io
Now, it wasn't hassle free as Telegram doesn't send verification codes for (this is my guess) whatever gets flagged as suspicious attempts. It took me something like 4 number rotations and I had to do this on Telegram's iPhone app but it worked. Now, onlinesim has a system that will refund you the money if you don't use the number and whenever Telegram doesn't send you a verification code you can simply refund your purchase and try a different phone number.