One of my biggest goals of jailbreaking the iPad was to be able to use WhatsApp on it. As you know, the messaging client only works on mobile phones, and the key to installing WhatsApp is to trick it into thinking that it is operating from a phone, and not a tablet.
Here's what I did to install WhatsApp on iOS 6.1.
Step 1: Download and install the latest version of WhatsPad from the Cydia store.
Step 2: Download the latest WhatsApp.ipa (at this point of publication, it's 2.8.7). The iPad is smart to the point that it recognizes older, outdated .ipa installation packages. If you try to run anything older than 2.8.7, the iPad will bring up a "Please update to the latest WhatsApp" error message.
Step 3. Connect your iPad to your computer. Use a third party installer (like iFunBox) to install the .ipa package onto your iPad.
Step 4. You now have the app on your iPad. Now you need to verify your app. Verification requires you to key in a code that will be sent to a mobile number. This is the main problem with installing WhatsApp on iOS6.1: you need a working mobile number just to verify the app. You can't escape the verification by putting in a house or office number.
Step 5: This next point is very important. Do not use your own phone number to verify if you already are a WhatsApp user! If you do, your existing WhatsApp will be logged out--removing you from every chat group that you are a part of and erasing your chats. I learnt this the hard way, and I don't want anyone else to suffer! Use a spare mobile number to verify the app. My mother is a technophobic retiree who will never touch a smart phone, so I just used her mobile number.
If you really want to, I suggest buying a pre-paid SIM card for the sole purpose of verification. Yes, I know it doesn't make this method free, but I think the benefits of having WhatsApp on the iPad more than make up for the cost involved.
I have hosted the latest WhatsApp.ipa package here for your download.
You might want to improve the experience of WhatsApp on the iPad by using either of the additional tweaks below:
RetinaPad - You know how the 2x view of iPhone apps on the iPad look grainy and reminds you of your old Gameboy display? This tweak fixes the display by correcting the distortion and making your iPhone apps look it's in HD on the iPad.
FullForce - This tweak forces an app to conform to the dimensions of the iPad's display dimensions and uses the native iPad keyboard (instead of the iPhone keyboard).
For further reading (legacy methods):
Installing the WhatsPad tweak (Redmond Pie)
Using iPhone configuration utility (Justin.my)