Generally cell phone service providers gives 2 types of data packs, 2G and 3G. There 2G packs are cheap but 3G are so expensive. Here is a trick that can change 2G data balance into 3G data balance. I have tested this in Reliance India mobile, but I think this trick can work in other service providers too.
Recharge by a 2G large size data pack with a sufficient validity that is sufficient to use by you. For example I have recharged my reliance GSM network phone with 5GB 2G data that was having validity of 30 days.
Now recharge with a cheapest 3G pack that is having a sufficient validity. For example I have recharged my reliance GSM network phone with 300MB that was having validity of 30 days. When you will use this 3G data, after finishing this your existing 2G data will also behave as 3G data. And you will be able to use your 2G data as 3G until validity of 3G pack will have not expired.
You should use HSPA/3G mode to use 3G speed.
There is no working guarantee of this trick, should try with less amount packs
- Comment here if you have tested the trick.