Good, it is nice to see some new twist on an old puzzle.
As a first hint: the underlying code has also been used in the puzzle
"What comes next in this sequence?" posted by Gilles in November 2014.
It also shows up in some books of Martin Gardner published in the 1960s.
Now the answer to the Mission Impossible puzzle is:
The code-name of the courier is Enzo.
Ethan Hunt should intercept the courier in Tennessee.
Motivation of answer:
0=Z(ero), 1=O(ne), 2=T(wo), 3=T(hree), 4=F(our), 5=F(ive), 6=S(ix), etc.
Under this substitution code, the message to Ethan becomes
8901 6892 31 389987688 782 154 6119
ENZO SENT TO TENNESSEE. SET OFF SOON!