Fallout New Vegas. The composer is a German dude named Gerhard Trede. He appears to have been someone from the Swing Era(?) who later got into electronic music. Or I could be completely wrong about that. Either way, I really love "Hallo, Mister X." Here is a short bio of Trede:
Gerhard Trede was a successful composer in Germany from the 1950’s through the 1970’s. He composed for a variety of German television programs and documentaries, and composed music for the Selected Sound Library, a producer of “library music” or “production music” used by producers of television, radio, and film because it offers simple flat licensing terms. (source)
Before checking into it, I thought it was possibly something Billy May did, due in part to the section when the saxophones come in for the first time. That sounds very Billy May-esque to me, and the song is very "big and brassy" (another trademark of a Billy May arrangement) overall.