It's worth noting that many landline phones now allow you to enter a number that you're intending to call, then pressing the call button at which point the number is automatically dialed.
If the dial tone is heard at all, it is for a very brief period, and might be entirely missed. This would make the scam you're describing even more readily achieved.
... the autodial feature may well be waiting for dialtone in order to dial. I've not looked into this and you're probably best off testing this yourself on your own equipment.
If the dial tone is heard at all, it is for a very brief period, and might be entirely missed. This would make the scam you're describing even more readily achieved.