Understanding How HotSpot@Home Works

Now that you own a cell phone, why continue paying for a landline at home? Chances are, it's because you struggle with poor reception inside your house. Cell phones communicate with the closest cellular tower using radio waves, but if your home has aluminum siding or was built with thick concrete and rebar, the signal has trouble getting through the walls [source: The-Cell-Phone-Advisor.com].

In June 2007, T-Mobile launched HotSpot@Home, a service designed to enhance indoor cell reception by allowing users to place and receive calls over their home WiFi network, alongside the standard cellular network.

T-Mobile isn't the only U.S. cellular provider offering a combined cellular/WiFi solution—Cincinnati Bell has also launched a similar service [source: GigaOM]. However, T-Mobile remains the largest, so this article will focus on their HotSpot@Home service.

Here’s what you’ll need to get started with HotSpot@Home:

If you already own an 802.11b/g wireless router, you don’t need to purchase a new one. However, if you don’t have one, T-Mobile offers its own wireless routers optimized to prioritize voice traffic over data. This feature is handy if you’re downloading a large file while on a call—your call will remain clear while the file just takes a little longer to download.

Setting up HotSpot@Home is straightforward:

Immediately, the cell phone should detect and connect to the home WiFi network [source: Phone Scoop]. You’ll notice a symbol in the top-left corner of your phone's display. The WiFi signal strength is shown as a small orange circle with radio waves extending to the right. The more waves visible, the stronger the signal.

Now that you're connected, let’s review how to use the HotSpot@Home service.

How to Use HotSpot@Home

Once connected to the home WiFi network, simply use your cell phone as you normally would. All typical calling features, such as caller ID, three-way calling, and call waiting, are available when using the WiFi network for calls [source: New York Times]. However, web-based activities like checking email or browsing the Internet cannot be done over the home WiFi network. Data transfers must be handled through the regular cellular network.

While using the HotSpot@Home service, any call made or received over the WiFi network will remain on that network as long as the phone stays within a strong WiFi signal. If you walk out of range of the wireless router, the signal will gradually weaken until the phone automatically switches to the cellular network. This process, called a "handoff," happens seamlessly, often without you noticing the change [source: engadget mobile].

The same happens when you re-enter your home. As soon as the WiFi signal becomes strong enough, the phone will automatically switch from the cellular network back to the home WiFi network.

There are many benefits to using a service like HotSpot@Home, with the main one being cost. By paying an additional $9.99 per month for the HotSpot@Home Add-On, you can make unlimited nationwide calls over WiFi, any time of day. Calls made or received on the WiFi network will be billed as WiFi calls, even if you switch to the cellular network during the call [source: New York Times].

For instance, if you call the office from home and then drive an hour to work while continuing the conversation, the entire call will be billed as a WiFi call. WiFi calls don’t use up minutes from your regular plan if you’ve subscribed to the HotSpot@Home Add-On. Without the Add-On, calls made from WiFi will be charged to your regular calling plan, including any applicable peak-hour or nighttime/weekend rates.

Another financial benefit of HotSpot@Home is the ability to eliminate your landline telephone, along with its additional local and long-distance fees.

With HotSpot@Home, you can make calls from any available WiFi network, not just your home network. The dual-mode phones make it easy to search for available WiFi networks [source: Phone Scoop]. If a network requires a password, simply enter it into the phone. The phone also keeps a record of the WiFi networks you've connected to, including their passwords, so it can automatically connect to them in the future.

In addition, T-Mobile has set up over 8,000 HotSpots across the U.S. in popular spots like Starbucks coffee shops and FedEx Kinko’s offices. T-Mobile’s dual-mode phones automatically connect to these WiFi networks without the need for searching or entering a password.

Now let’s dive into the technology that powers the combined cellular/WiFi networks.

HotSpot@Home Technology

HotSpot@Home leverages three rapidly advancing telecommunications technologies: dual-mode cell phones, home WiFi networks, and wireless VoIP (Voice over Internet Protocol) telephony.

Wireless VoIP telephony connects a cell phone to the wider network using an IP network, rather than relying on cellular towers and switches. Dual-mode cell phones, which include WiFi radios, can access these IP networks via WiFi routers. For a more in-depth understanding of how WiFi VoIP operates, take a look at How WiFi Phones Work.

Dual-mode cell phones use a technology standard called UMA (Unlicensed Mobile Access) to communicate over home WiFi networks. A UMA-enabled phone can connect to any unlicensed WiFi network, which operates over a free and unrestricted radio frequency. For instance, 802.11b/g routers operate on the unlicensed 2.4GHz spectrum. Licensed spectrums are purchased by companies or government bodies for exclusive use [source: WiMax.com].

Dual-mode phones, with both cellular and WiFi radios, are capable of making calls over two distinct networks: the Cellular Radio Access Network (RAN) and the Unlicensed Mobile Access Network (UMAN) [source: UMA Technology]. The phone automatically selects the network with the strongest signal, whether cellular or WiFi.

A Cellular Radio Access Network (RAN) represents the conventional cellular network, which relies on a network of cellular towers and switching stations. For an in-depth explanation of how cell phones function over a Cellular Radio Access Network (RAN), refer to How Cell Phones Work.

Here’s how a dual-mode cell phone connects to the mobile network through an Unlicensed Mobile Access Network (UMAN):

If a dual-mode cell phone moves out of the WiFi network’s coverage area, it automatically switches to the cellular-radio network without any disruption in service [source: UMA Technology].

Routing calls through two different mobile networks is actually a significant cost-saving strategy for cellular service providers. The only way to enhance coverage and handle heavy traffic on a traditional cellular network is by constructing additional cellular towers [source: New York Times]. However, with HotSpot@Home, T-Mobile can reroute a large portion of that traffic onto broadband Internet networks—networks they do not own and therefore don’t have to maintain.

Services like HotSpot@Home are emerging as a major trend in telecommunications. In the rapidly expanding cell phone industry, dual-mode phones are experiencing the fastest growth worldwide [source: cellular-news]. Infonetics Research forecasts a compound annual growth rate of 198 percent for dual-mode phone sales between 2006 and 2010.