Call the customer care, they will deliver the sim to you usually within 24hrs, also for your question, 3g is much better as where ever the 3g network is available it will run on 3g and even where it is not available it will run on speeds better than what EDGE one will. I knew a friend who was using the EDGE one and he got speeds like 20 or 30 kbps, its just theoritically possible for it to support 144kbps.
Also, try websites like flipkart.com or ebay.com or
ebay.in or others to buy 'unlocked' usb modems, they are similar to vodafone ones, just cheaper, better build and much more flexible as you can run them on any company's sim, postpaid or prepaid, with any data plan active on the sim. This way, you can use two sim card for both edge or 3g with a single modem.
Modems which are sold by vodafone are of good companies but still are of pathetic quality, sky high prices, slow as anything. Also, its only in india that vodafone sells such modems, outside of the country they sell the best under their brand.
Unlocked modems from companies like ZTE or
Huawei are the best, unlocked huawei e220 is a great option.(see the link below)
http://www.ebay.com/itm/HUAWEI-E220-HSDPA-UTMS-3G-USB-MODEM-to-7-2Mbps-UNLOCKED-/250818953485?pt=LH_DefaultDomain_0&hash=item3a65f9810d#ht_5050wt_910
(free shipping)