This can be confusing, especially since the options in the US are somewhat different from those in Europe, at least in terms of cost. For the US'ers, the following holds.
() It's important to distinguish between a dedicated "mobile hotspot" device (about the size of a playing card and 1/4 inch thick) and hotspot functionality "built-in" to a smartphone. The former is a separate device with its own phone number and data plan, typically a 1-2 year contract that cannot be turned off/on on a monthly basis. Mine is $50 for a 5 gig ceiling.
() A separate monthly "tethering" charge (about $20USD per month) from the carrier typically applies unless one uses a method to "root" or "jailbreak" one's phone, a practice that may violate one's contract with the carrier and lead to additional charges. However, the tethering charge may increase the download ceiling for your smartphone data plan. (Depends on carrier.)
() Some of the newest smartphones (Android) enable tethering at 4G speeds. Typically, this is much faster than the 3G speeds available with iPhones or 3G iPads. However, the speeds are somewhat slower (according to tests I've seen) than dedicated mobile hotspots in 4G coverage areas. (My dedicated mobile hotspot from Verizon typically gets download speeds 7 to 10 times greater than an equivalent 3G signal. According to some tests I've seen, tethered 4G speeds are about 30-50% less than the dedicated mobile hotspots but still much faster than 3G speeds.)
() Unlike the monthly cancellation/activation data plan available for the iPad, one typically pays for an extended data contract (1-2 years) for a smartphone or dedicated mobile hotspot. That's irrelevant, of course, if one already pays for a long-term data plan on a phone or a dedicated mobile hotspot.
() The battery drain on the phone/dedicated mobile hotspot is worth taking into consideration. My dedicated mobile hotspot from Verizon typically runs about 4-5 hours in 4G/LTE service areas and about an hour longer in 3G areas. That is considerably less than the iPad but it really doesn't matter to me since I'm seldom away from a power source for more than 4 hours.
() AFAIK, smartphones and dedicated mobile hotspots cannot provide the GPS functionality that is built into the iPad's 3G hardware. However, there are GPS receivers available for less than $100 that integrate with the iPad to provide even better GPS reception than the iPad. Since the price difference for a 3G iPad in the US is $130, the attached GPS receiver can be both more economical and provide better performance.
but in Dubai data plan is very costly 
