Yes, there is, when you leave Bandung Airport - Rp 100,000
It's a damn nuisance, don't understand why they can't charge it into the ticket price.
For Vietnam, lagi teruk - you have to be prepared with USD30.

Yeah. I agree with u. I normally buy local SIM card but I also open my hp international roaming since I have 2 phone. Maxis and Celcom. Celcom offer me good deal for international roaming.

you are welcome but standard is 12hrs which for IDR400k is a good deal and it covers driver and petrol but you will need to pay for toll and parking fees(usually about IDR2500/hr depends on the location) and at Tangkuban Perahu each tourist will be charged IDR50K and the van IDR12500 entrance fees. At the top if you want a guided tour to reach the hotspring you will be charged IDR300K/hr and if exceed 1hr you need to pay the guide seperately. Beware it will normally take more than 1hr to complete the journey and beside the guide there will be at least few more person following you and they will pester you to buy souvenirs which are generally grossly overpriced.

I think you can but not from the top but at the end of the journey to the hotspring, because I saw lots of local doing that but we did not check further. Maybe you can try and update us later

You can walk around by yourself at Tangkuban Perahu. You don't really need guide unless if you want to go for the tracking tour down to the crater.

But pls be very careful when u buy souvenirs in Tangkuban Perahu. The seller can be very persistent and follow u around. Don't scold them or show them your anger. Just smile and wave your hand  and say tak mau or tidak apa.

Normally the vehicle rental include petrol,parking and toll unless they mentioned it before hand to you.