Do you have an old radio that looks great but for which you have no practical use? If you're not afraid of a soldering iron you can add a new solid-state amplifier to give you a standard 3.5mm input jack for your smartphone or MP3 player.
Masculinity blog The Art of Manliness details adding a new amplifier to a vintage radio as a great project for those interested in electronics. You'll need a 12-volt power supply, a soldering iron, 22-gauge copper-strand wire, and a 3.5mm audio cable; all of these you should be able to track down at Jaycar, as well as an amplifier that will work with vintage radios. You can buy such an amp here as a kit for $US20 or fully assembled for $US26.
All you're doing is removing the existing wire connections from the speaker and volume control from the existing tube amp and soldering these to the new amplifier. Full step-by-step instructions with photos can be found at the link below.
Two caveats: Make sure your vintage radio is not terribly valuable before you take it apart and also make sure the speaker in the old radio is a permanent magnetic speaker and not an earlier electrodynamic speaker that won't work with the new amp. If two or threee wires are connected to the speaker, it's a permanent magnetic speaker. If you're stuck with an electrodynamic speaker, you can buy a new 2-inch speaker for about $US4.
How to Make an Old-Time Radio Into an Mp3 Player Speaker [The Art of Manliness]