Mobile broadband coverage can vary from place to place and from network to network. In a similar way that you may find poor mobile phone reception in some areas, the same problem can affect mobile broadband. For this reason, it is important to ensure that the network you are thinking of using has good coverage in the areas you intend to use it.
Mobile broadband can use different technologies to when you make a phone call on your mobile, however coverage will often be very similar for both. Indeed, mobile phones often support both 3G and 4G for accessing the Internet on your phone, so coverage of these will help indicated mobile broadband coverage.
Each mobile network has the ability to check coverage on their website before you buy. If possible, find a friend or family member who uses the mobile network you prefer and see what the signal strength is like on their phone. If it indicates good 3G or 4G reception, then this should offer good mobile broadband reception. (3.5G reception is often only shown when you have a data connection active, so you may need to open up the web browser on the phone to see this). You can find links to each coverage checker for the UK networks here which will give an indication of the mobile coverage available:
Note, now that T-Mobile and Orange have joined forces under EE, their coverage should be the same.
3G is one technology which is used for mobile broadband, but is also used on mobile phones for data and things like video calls so can be listed separately. If your area has good 3G coverage, you should be able to get mobile broadband speeds of a few meg. HSPA is also used which provides faster speeds, although this can vary between networks. Cities and urban areas are more likely to find the faster HSPA and 4G services which offer speeds of several or tens of megabits per second.
Mobile phones use wireless signals and the range and signal strength of these will vary depending on how far you are away from the transmitter, the transmit power, and if there are things in the way that will block the signal. The best signal is obtained if you have direct line of sight to the mobile phone transmitter, or if there is one very close by (for example in your road). Being inside a building will reduce the signal strength as walls and windows will block some of the signal and can cause reflections of the signal which cause interference. 4G networks should improve indoor coverage as they use lower frequencies which travel into buildings more easily.
Mobile broadband falls back to using EDGE (if available) or GPRS (a 2.G technology) if it can't get a 3G signal. These can be used for mobile broadband, but are often slow and may not provide a good quality of service. If travelling on a train, you may notice the signal varies from 3.5G down to GPRS (or no signal) during a journey, and this can be frustrating if trying to work online. If you plan to use mobile broadband at home or at work and can only get GPRS, you may want to consider getting fixed line broadband instead.