Yes, Samsung Metro XL does have call conference facility.
You can use Facebook which is pre-installed on this phone but you can not use WhatsApp in this phone.
Yes, Metro XL does have speaker, which is located on the back side of the phone.
Yes, Samsung Metro XL does support the Tamil language.
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.