At 35.20, Standish is trying to tell Lamb what she learned in the chess game, and he hangs up on her. You can hear a dial tone from her cell phone. Cell phones don't have dial tones.
It makes no sense for the Russian sleeper agents to leave River alive if their goal is to carry out a terrorist attack with a massive death toll that he knows about and could potentially thwart, or at the very least bear witness to their involvement afterwards. So it is out of character for River not to get suspicious about getting set-up when he wakes up alive.