Yes, and per previous reports the subject being discussed was the Obama sanctions on Russia. Flynn was supposedly fired for lying to Pence that they weren't discussed on that phone call, at all, leading Pence to state that no Trump official had done so, But supposedly Sally Yates called Pence and/or Trump and told them they had the tape of Flynn, which led to the firing, and now the charge of lying to the FBI as they had questioned him as part of the vetting for National Security Advisor.
Debates exist about how deep Flynn's conversations about the sanctions went, and if they were made while he was on vacation in the Caribbean or not. Per supposed leaks nothing was actually promised to the Russians, especially not in a quid pro quo manner, but no transcripts or audio has ever been released.
But most importantly, whatever discussions that Flynn had with the Russians, they were apparently made completely on his own, based on Trump and Pence's assertions that no promises were made by anyone to their knowledge, which would certainly have included themselves. And they followed through with the quick firing of Flynn for what might have been an otherwise inconsequential lie.
Where Mueller takes this now is anyone's guess, but based on all the known facts so far, he seems extremely intent on charging Trump team members with anything he can possibly find, while turning a complete blind eye to anyone related to the Clinton campaign.
Dunno of course ... but seems to me this sets up a precedent about lying to Mueller that should be applied to Obama + Clinton folks. This sequence of events sets up for something major to drop this coming week, hopefully after the tax bill is passed and John McCain’s curiously switching boots isn’t a factor here.