Q: A lot of new iPads if not all have problems activating Personal Hotspot. Any solution on this?

– Marc (via Twitter)
A: Firstly, keep in mind that the Personal Hotspot feature is only supported on the new, third-generation iPad; it is not available on older models, even with the latest iOS updates.
Even if you have a supported iPad model, however, the availability of the Personal Hotspot option is controlled by your carrier and the configuration file supplied by your carrier for whatever microSIM card you are using. It’s also important to remember that just because a carrier offers the Personal Hotspot feature for the iPhone, it does not mean that it will automatically be available for the iPad as well.
Further, some carriers include Personal Hotspot access as part of all data plans, while other carriers either charge extra for this feature or limit to only specific data plans. In these cases, the Personal Hotspot option will appear on your iPad, but you may not be able to activate it unless you are on the necessary plan.
Most of the problems that we have encountered with users enabling Personal Hotspot are carrier-specific, and it may therefore be necessary to contact your carrier or Apple Support directly.
Apple maintains a support article on Locating Wireless Carriers that includes details on which iPhone and iPad services are offered by which carriers. Unfortunately, this article is specific to the iPhone, and doesn’t indicate those carriers which may not offer Personal Hotspot for the iPad, nor what the specific plan requirements are for Personal Hotspot. You will need to call your specific carrier to find out if the plan you are on is eligible for Personal Hotspot.
Apple and supported iPad carriers also routinely release updates to their configuration files, distributed either over the air or via iTunes depending on the carrier and region. If you are on a supported carrier and plan and are still having problems with the Personal Hotspot feature, you can try Updating your Carrier Settings to see if that helps.
In some cases, resetting the network settings on your iPad may also be necessary to cause the Personal Hotspot option to appear or to properly enable. This option is found in the Settings app under General, Reset.
This option only resets your network-related settings and does not affect any other data on your device, although it will be restarted immediately after you select the option. Note that your configured Wi-Fi networks are part of your network settings, however, and will need to be reconfigured after doing this.