Models
IPad, the popular tablet PC from Apple is currently available in 2 variants, the WiFi only model and the Wifi plus 3G model. There is no specific model number for each though, users can simply call their unit “WiFi only” or “WiFi + 3G” model.

Similarities
The 2 variants are pretty much alike i,e. in terms of form factor, dimensions, screen size, processor, operating system and all other hardware components and software. On the other hand, the chosen model also may vary in terms of its storage capacity. Users can choose from different available storage capacity – 16 GB or 32 GB or 64GB. Of course higher built-in storage capacity means higher price.

iPad models

Differences
As the model names imply, the Wifi only model connects on a network through its WLAN and the WiFi + 3G model can utilize both available WiFi and 3G connections in the location.
The Wifi + 3G models weighs a bit heavier than the wiFi model. The former weighs 1.5 pound (680 grams) while the latter weighs 1.6 pound (730 grams)

Comparison Table

WiFi WiFi + 3G
OS iOS 4.2.1 iOS 4.2.1
Processor 1 GHz Apple A4 1 GHz Apple A4
Storage 16GB / 32 GB / 64 GB 16GB / 32 GB / 64 GB
Screen 9.7”multitouch

1024 × 768 pixels

9.7”multitouch

1024 × 768 pixels

Dimensions (9.56) x (7.47) x (0.5) inches (9.56) x (7.47) x (0.5) inches
Connectivity WiFi, USB 2.0, Bluetooth WiFi, USB 2.0, Bluetooth
Battery 10 Hrs video140 Hrs audio

30 days Standby

10 Hrs video140 Hrs audio

30 days Standby

Weight 1.5 pound (680 grams) 1.6 pound (730 grams)
Connectivity WiFi WiFi and 3G

Update:
The next Generation iPad, the iPad 2 has been released. It also comes in variants like the iPad 1 i.e. available as WiFi only and WiFi plus 3G. In addition, variants for storage size are available alike.