Yes, Samsung Metro XL does have call conference facility.
No. Samsung Metro XL does not support Nimbuzz chat messenger.
No. Java apps are not supported.
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.
You can use Facebook which is pre-installed on this phone but you can not use WhatsApp in this phone.