I spend quite a lot of time on calling my colleagues in US or UK (I am in Hungary), which can result in quite exorbitant phone bills. I tried to fix this lately by looking for IP telephony solutions for iPhone - I often have conference calls lasting upward of half an hour, and up to even two hours, so I don't want to be confined to my desk or any other physical location. I will often walk up and down in the apartment, subconsciously tracing patterns of the carpets with my feet (it's funny when I consciously realize I'm doing it), staring out of various windows at the sky, sometimes sprawling on a sofa and so forth. (Hey, working from home has its perks!). So, I need mobility within the apartment, hence I still want to use the phone.
Now, Skype would be the obvious choice - for a flat fee of 10.29 EUR/month I can get unlimited calls to both US and UK numbers. Major hurdle is that Skype ships no client for the iPhone. Fring actually does the job, it is a multiprotocol chat/voice client for iPhone (and some other phones) that supports Skype accounts too. Voice quality is not particularly good, but it's within tolerable. Fring however lacks an essential (for me) feature - it does not provide a DTMF keypad. I always dial into the company conference center, and must be able to punch in the conference number I wish to join. Fring can't do it. I can still use it to call direct extensions, but the bulk of my calls is through the conference system, and it's a no-go. I asked Fring support, and all they told me was:
Currently, it is not available to dial DTMF sounds on fring, this should be implemented in future versions.For the record, Skype desktop client does have a DTMF keypad.
Next choice is TruPhone. They offer a client for iPhone (and also a bunch of other makers' devices). TruPhone operates their own call service, much like Skype does, and while there's no flat-fee subscription model, their 0.06 USD/minute plan is sure quite attractive (heck, even calling numbers within my cell provider's network, T-Mobile Hungary, is more expensive than that!). The voice quality is very good, even better than cellphone (one coworker remarked after I first used it to dial in to a conference that I sounded much clearer than I usually do). The client app also has a muting button and a DTMF keypad, the first useful, the second essential for conferencing. It would all be rosy, if only the client weren't extremely buggy. Sometime, with iPhone OS 2.1, the UI would slow down (you could see it animate scrolls pixel by pixel) and it'll then claim there's not enough memory. iPhone OS 2.2 seem to have fixed that, but now it instead often complains that it can't find "Wi-Fi coverage" (even though the iPhone itself clearly sees the network). The aforementioned DTMF keypad has the tendency to not react to touch, or conversely, to get jammed as if I touched the key but didn't lift my finger, sending a prolonged shrieking "beeeeep" of that particular number key tone through the earphones into my skull, full volume. (The iPhone built-in phone app nicely tones down the DTMF beeps on my end of the line, so I still have an audio feedback that I'm typing them, but don't hear them full-volume). Regardless, the "low memory" and "unable to find wi-fi" are the most critical problems - even turning the phone off and on again doesn't always help it with its wi-fi disorientation syndrome (and mind you, I should never be forced to power cycle my phone just to use an app!).
So, it's a mixed bag. I'd use Fring if it had a DTMF keypad because of a flat-rate unlimited calls provided by Skype. The second best right now is TruPhone, which provides very good voice quality and otherwise pleasant service with low pay-as-you-go rates, but their iPhone client is bordering on unusable because of all the bugs. I'll be eagerly awaiting app updates to both.