Who said it has half the functions.
The 6610 is aimed for the executives who won't be interested with the screensaver things. The 3100 is aimed for the youth who want to show off.
Here is a list of Functions present in the 6610 not available in the 3100:
1. Infra Red: Arguably the most useful things for people who want to remain connected without the hassles of the wires. The 6610 has got IR for transfer of V-cards and for connectivity with PCs. The 3100 lacks the Infra red connection.
Advantage: This is a great use for people connecting to the desktop storing their personal contacts etc. they don't need to shell out another $50 to buy a cable, and it can be used on virtually any PC with an IR connection, which many have.
2. GPRS modem: And this one is a boon for the people who are on the move and want the work done fast. 6610 can be used as a PC modem, ie connected to the computer and used to surf the internet on the PC with the normal GPRS Provider(ie Service Provider). The 3100 cannot be used as a modem.
Advantage: Great for mobile people, who use their laptops often for surfing the net. No tensions of having to find the phoneline in the hotel room and all. If the laptop and the mobile are both adequately charged then you can even surf the Net in the bus, car, train, above the train etc...
3. FM Radio: This one isn't that important but still a feature nonetheless, for those on the move who want to listen to some good ol' melodies or the raging new ones. It's free also.
Advantage: No real advantage, but if you don't own a laptop this can be a great past time.
4. Speakerphone: I don't think the Nokia 3100 has a speakerphone. Correct me if I'm wrong. The 6610 has one, and it is very useful.
Advantage: Speakerphone is handy if your ear starts paining due to prolonged contact of the phone to the ear. Just activate it, and then you can talk at a good distance of max. 2 feet.
Now tell me do you still like a stupid animated screensaver, rather than such goody good functions. If yes, then get the 3100 as the 6610 isn't meant for you!