A recent mentioned the wide array of hardware devices one can use with a  account, the fact that many of them have limited Mac compatibility, and the dearth of information available to help Mac users choose among them. Since I recently went through the exercise of researching (and eventually purchasing) such hardware myself, I wanted to share my own experiences. I admit that my criteria for selecting telephone hardware are atypical, but I suspect that many of my findings will be generally useful nonetheless.
My own switch to Skype as a primary means of telephone communication was prompted by my recent move to France. Before the move, my wife and I looked long and hard at our telephone needs, since we knew we'd be spending lots of time on the phone with people back in North America. I'd resisted Skype for a long time because my only experience with it involved being inconveniently tethered to my computer with a wired headset, and I felt that the process of making and receiving calls exclusively with Skype would be needlessly inconvenient. But when I looked at Skype's prices compared to other providers, and the range of available hardware options, I realized I had been operating under some misconceptions. I could have a fairly painless telephone experience with Skype if I put the pieces together in the right way.
That decision made, we signed up for two personal SkypeIn numbers (plus one for our business) at $60 each per year, allowing us to receive phone calls from ordinary phones at U.S. phone numbers. We also got prepaid SkypeOut accounts, which let us make outgoing calls to ordinary phones (in every country we currently need to call) at 2.1 cents per minute. (Unfortunately, the terms of service for Skype Unlimited, which costs $29.95 per year for unlimited calls to the United States and Canada, don't permit its use from outside North America.)
Sifting Through the Hardware Options -- That left hardware - what sort of apparatus we'd use for audio input and output and dialing. This was a challenging puzzle to solve. The range of options is immense, but every piece of hardware required one or more tradeoffs among price, quality, and convenience. One consideration that factored strongly into our thinking was overall compactness. We'd decided to take with us only what could fit in our luggage in order to avoid the expense and hassle of shipping our possessions across the ocean in some other way, so eliminating bulk and weight (as well as any nonessential electrical items, which would require special adapters) was key.
Here are the options we considered and why we decided what we did:
Having ruled out the Wi-Fi handsets and cordless phones, we realized that we'd be stuck with devices that would require the use of a computer. However, we still had a wide range of options:
Simply performing the analog-to-digital and digital-to-analog conversion of sound to operate the microphone and speaker, respectively, is not problematic: plenty of USB audio devices work brilliantly on any modern Mac without any extra drivers or other software at all. It's the connection to Skype in particular that requires software mediation - software is needed to take the input from the buttons on the handset and send them to Skype, or to tell the handset to ring when a Skype call comes in, for example. And few USB handsets offer such Mac software.
Choosing a Handset --  lists three Mac-compatible USB handsets (all corded): The , the , and , with software download links for each. Of these, only the USRobotics model was actually for sale on Skype's site, and at $57.95, it seemed awfully expensive for what it was. So I decided to look elsewhere.
A Google search led me to, which features a page with Mac-compatible Skype devices of all sorts, along with instructions and software download links. We decided to get two different Yealink corded models, both fairly basic (but also fairly cheap): a  for $22.95 and a P8D for $29.95. I would have liked something cordless, of course, but a handset cord bothers me much less than headset cords, and in any case, the cordless options involved greater expense and more physical components than I preferred.
When the two phones arrived, I immediately installed the software and tried both of them out. The USB-P1K worked; the P8D did not - it appeared not to recognize the Mac software at all (or vice-versa). I sent an email message to VON-Phone.com, and the owner replied that he had just tried out the phone on his own Mac and had the same problem. He offered to send me a different Yealink model, the, and didn't even mention that it sold for $10 more; I brought that up myself and offered to pay the difference. He sent the new phone the same day without waiting to get the old one back, and even included a postage-paid envelope for me to return the one that didn't work. Shortly thereafter, the P8D was removed from their list of Mac-compatible devices. That experience gave me warm fuzzy feelings about VON-Phone.com; it's exactly the way good customer service should work.
Hardware and Software Experiences -- Both of these phones use software from Yealink called SkyMACMate to enable the phones to talk to Skype - meaning that both programs must be running in order for you to use the handsets. SkyMACMate version 184.108.40.206 is a functional but unimpressive little program. Its single window gives you volume controls for speaker and microphone - and nothing else. If you want it to run all the time, you have to add it to your Login Items list manually. I'd have preferred a background application that was completely invisible, with a preference pane to adjust the settings if necessary. (Note that you must also configure Skype to use the handsets for input, output, and ringing by choosing USB Audio Device from each of the three pop-up menus in the Audio pane of Skype's Preferences window.)
With the software installed and running, the experience of using the two phones is remarkably different, despite their superficial similarities. With the USB-P1K, the handset is essentially a remote control for Skype's on-screen interface. That is to say, pressing the arrow keys makes the Skype application scroll through its contact list, and certain other keys similarly "pass through" to the equivalent buttons in the Skype windows. Numbers you dial on the phone's keypad do show up on its LCD display rather than on the screen, but otherwise it's somewhat disorienting to use the handset when you also have to look at something on your computer. The P5D, on the other hand, functions much more like a regular phone. Its LCD display lists the names in my Skype contact list, and I can scroll through them and call any of them without ever having to look at my computer screen.
Both phones have respectable, though not stellar, sound quality. They're about what you might expect for under $30: cheap plastic devices without a lot of attention to style, detail or extra features, but as corded phones go, we've found them entirely adequate.
I'm a bit less happy with the software situation. SkyMACMate is not a universal binary, though I'm unsure how much of a performance penalty that produces on my MacBook Pro. I've read numerous reports of problems with this software, but they appear to occur mainly with the use of the USB-RJ11 Skype Adapter mentioned earlier, rather than with handsets like we have. I have experienced a couple of random crashes, and there is some evidence to suggest that a memory leak is at fault, but as long as I quit and relaunch the program once a day or so, it seems to behave. Ordinarily I'd say that's more bother than I'd be willing to go through on behalf of poorly written software, but the other options available to me (such as replacing this with an entirely different brand) would also involve some bother, not to mention expense. I'll keep my fingers crossed for a software update.
The One and the Many -- Having done still more research since making my purchase, I've become aware of some interesting facts about Mac-compatible USB Skype handsets. Yealink, a smallish Chinese OEM, is the manufacturer of both the Simplyphone and USRobotics handset models, among numerous others, all of which use the same software - though Simplyphone rebrands theirs as CallMe. (The Yealink name, by the way, doesn't appear on their phones; some of them have the Radian brand and others, like the USB-P1K, are unbranded. The USRobotics USR9601 handset is the same as the P8D I had difficulties with, though it's unclear whether their branded version has any electronic differences that may enable it to work while the ones available from VON-Phone.com don't.)
Clearly, Mac software is not Yealink's core focus. But if you're unwilling to use the SkyMACMate software, you significantly reduce the number of Mac-compatible USB handsets from which you can choose. Other than Yealink-manufactured brands, I'm currently aware of several models; the ; a few phones from ; the  (seemingly available only from the UK); and the . I've tried none of these yet, so I can't comment on their performance or the robustness of their software.
Of course, I'm certainly in the minority in attributing such great importance to limiting the number, size, and weight of my gadgets. If you don't mind having an extra box or two, a USB phone adapter may be more to your liking, and if your budget is higher than ours was, you can bypass the Mac software issue entirely by buying one of the cordless Skype phones that plugs directly into an Ethernet connection.