Welcome to the Forum. I am sure that you will find everyone here happy to help with any questions you may have. I'll start off trying to answer some of the points that you raise and I'm sure other Forum members will correct me if I make a mistake.
First of all, if you don't already have a copy, you should read the iPad User Guide, which you can download from the Internet; it's not supplied with the iPad.
You can get a copy here
http://manuals.info.apple.com/en_US/iPad_iOS4_User_Guide.pdf
It contains a wealth of valuable information about how to set up and use the iPad.
If you service provider does not yet have a 3G network, the iPad will run on 2G using what is known as either 'EDGE' (which means "Enhanced Data Rates for GSM Evolution ') or 'GPRS' (which means "General Packet Radio Service"). You will not get as good a data rate as you would on 3G - so this could be a problem for surfing the web - but email should be OK as long as no one sends you an email with a big attachment. However, you will need to check with your service provider what 'data plans' they have available. The iPad will automatically switch from 2G to 3G if it detects a 3G service is available. But check carefully about the cost of the data plan or you could end up with a big bill.
If you want to surf the web or send and receive email, then you need access to either 3G/2G or WiFi. So, if you are in an area where there is neither of these, you simply can't send or receive email or surf the web. But you can use the iPad for a whole range of other activities - for example reading books or documents, writing documents, listening to music etc. You can even write emails and save them to send later, when you do have access to WiFi or 3G/2G - and, of course, you can read emails that you have already received and that are stored on your iPad.
I'm sure that you'll find in Delhi that there are public WiFi networks available - most big cities have them these days, perhaps in coffee shops or shopping malls. Some are free (shops offer free WiFi to attract customers) and some you may have to subscribe to, but I'm sure you'll find some. The iPad will search for WiFi networks and tell you when it's found some and ask if you want to 'join' them. WiFi networks are either encrypted or unencrypted. Public networks - of the sort that I've just mentioned - are usually unencrypted and your iPad can 'join' them without needing an encryption 'key'. The iPad will show you, when it finds a WiFi network, which networks are encrypted (an icon of a padlock appears) and for these you need an encryption 'key' to unlock the network.
To use your iPad on 2G/3G you need a SIM card, similar to the one in your mobile 'phone. However, the iPad uses a new type of SIM card called a microSIM, which is much smaller than the regular SIM used by most mobile 'phones. You will need to check if your service provider offers microSIMs yet; they are new and not all service providers have them available yet. It is *possible* (though perhaps not recommended) to convert a normal SIM into a microSIM and I've seen some Forum posts from people in India who offer to do this. You can do it yourself but it's not recommended for people who don't have experience in this area.
As you point out, you can't really use the iPad as a 'phone, so you'll need to take your regular mobile 'phone with you. You can make calls over the Internet using Skype and similar Internet telephony services, but it won't really work if you don't have 3G.
Final piece of advice - really just repeating something I said earlier and I'm sure all Forum members will agree with - download the iPad manual and read it thoroughly. It is written by Apple and it contains a wealth of very valuable and essential information.
Don't hesitate to come back and ask any further questions that you may have. Enjoy your iPad, don't panic if things seem to go wrong in the early days.
Have fun
Tim
Scotland