Yes, Samsung Metro XL does have call conference facility.
You can change the size of the fonts in Metro XL.
Yes, Samsung Metro XL does have music player.
Samsung Metro is the better phone if we compare the specifications.
01) Metro XL does have 2MP front camera while Nokia 3310 does not have front camera.
02) Metro XL comes with 2.8 Inch display while Nokia 3310 has 2.4 Inch display.
Both phone comes with standard 1 Year brand warranty but Nokia 3310 comes with replacement warranty.
Yes, Metro XL comes with pre-installed Facebook App.