Expect a much wider variety of phones that you can use with @Home in the near future.
As much as half the mobile phones sold in 2012 will support Wi-Fi (see figure from ABI Research, and Gartner forecasts similar penetration), so you will start to have this feature built into your favorite phones. T-Mobile is way ahead of the curve in offering this service and, unfortunately, there are few phones that work with it. Most subscribers desire Wi-Fi on their handset (56% of users, [Wi-Fi Alliance and Kelton Research, 2007]), but few carriers are interested in providing it, as it provides an alternative, free method for subscribers to obtain data and load content onto their phones.T-Mobile will add phones with Wi-Fi that can be used with @Home. The BlackBerry Curve is a fine phone, but it’s not for everyone.

The number of Wi-Fi handsets is expected to double every two years (50% growth per year) [ABI Resrarch, 2009].Over 50 Wi-Fi enabled phones were certified in 2Q2008, which represented a significant increase-hopefully the start of a larger wave of devices. So, while your choices in mobile phones (and routers) are very limited today for Voice over Wi-Fi, you should have a lot of choice in a year or two.

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500 Million Wi-Fi Phones Sold in 2012 [ABI Research

In addition to Wi-Fi, an @Home handset also needs to support UMA (Unlicensed Mobile Access), the service that allows the phone to connect to the mobile operator’s network over the Wi-Fi connection. So, unfortunately, just any Wi-Fi capable GSM phone will not do. For a complete list of @Home phones, please see the list, below:

@Home Compatible Phones: (as of 20 October 2008)

• BlackBerry 8900 (“Javelin”) Curve update
• BlackBerry 8320 Curve
• BlackBerry 8820
• BlackBerry 8120 Pearl
• BlackBerry 8220 Pearl flip
• Nokia 6301
• Samsung Katalyst
• Samsung T339
• Samsung T409  (initial Hotspot @Home flip phone, no longer sold by T-Mobile)
• Nokia 6086       (initial Hotspot @Home flip phone, no longer sold by T-Mobile)
• NOT an unlocked GSM phone that includes UMA and Wi-Fi
  Technically possible, but in practice impossible. Only T-Mobile approved handsets will work, due to the tight connection of an approved app on the handset. I’m all for buying the (unlocked) handset that you want and running it on the network of your choice, but (as with the iPhone), this means that tightly coupled features will be lost.
• NOT your (Wi-Fi-enabled) T-Mobile Dash or T-Mobile Wing,
  since they do not support the necessary UMA (Unlicensed Mobile Access) client that works with @Home service.

Soon you will be able to readily identify devices that support Voice over Wi-Fi (like your @Home router) for personal use. The Wi-Fi Alliance is planing to certify devices in 2009, much as they currently certify devices for their support of other standards, such as faster speed (IEEE 802.11g and n). If you want to know more, please see the nice summary that Wirevoltion.com provided here.

Wi-Fi Certification labels

The @Home router is optimized for voice over the Wi-Fi network; T-Mobile and Linksys (Cisco) thoughtfully included enhancements over the usual Wi-Fi router to (a) reduce handset power consumption and (b) ensure best audio quality by prioritizing voice traffic. The T-Mobile-specific Linksys router ensures excellent quality transmission of voice over your Wireless LAN by including support for some new standards (Wireless Multimedia, or WMM) that allow you to reliably send media (voice, video) over the WLAN. These features are so valuable that the Wi-Fi industry has created a certification test to allow consumers to recognize that the device supports Voice over Wi-Fi. It’s called “Voice-Personal,” and it includes support for:

• Power Conservation
  (“WMM Power Save”)
• Voice traffic prioritized to enable high-quality audio transmission
  (“WMM Quality of Service”)
• Simultaneous voice calls with high quality
  (4 simultaneous calls are tested while the network is loaded with other data traffic, just like you’d experience in your home with other people using the Wi-Fi network while you attempt to talk over the same, shared network)

Note: Both your phone and the router need to support the feature for you to get the benefit. For example:When your BlackBerry Curve supports WMM Power Save and you connect to a public Wi-Fi hotspot (that lacks these features), you will not get the talk time that you enjoy at home.