A recent survey of new iPad owners sounding off on Twitter revealed that a whopping 26 percent were unhappy about the fact that the device couldn’t replace their iPhone. That got us thinking: What would it be like to spend a day with only the iPad?

With that challenge in mind, we (mostly) stuck our trusty iPhone 3GS away for a full day and “made do” with only the Wi-Fi model of iPad. As it turns out, it’s not as difficult as you might expect. We have yet to find any iPhone apps that don’t also run on the iPad — even seemingly more complex ones such as SlingPlayer Mobile or Skype work just fine — so most of the iPhone functionality can already be duplicated just by installing the same apps you already use.

It’s Not a Phone, Silly

The biggest trick was replicating the cell phone part of the equation — you know, the thing that makes the iPhone a phone to begin with. This would be a particular challenge for an iPad that only offers Wi-Fi wireless connectivity. (For comparison, we’ll be returning to this project later in the month when our 3G-equipped model arrives, to compare experiences on both.)

For the phone part of the experiment, we installed four apps: Skype, Fring, Truphone for iPad and VoiceCentral Black Swan, the Google Voice “weblication” that we first examined back in January, while it was still in beta. (It’s since available to all in both free and paid versions.) Since our testing place has ditched the landline, we had to do a little bit of cheating, using Black Swan to initiate outgoing calls and then pick up the iPhone to actually carry out the conversation.

Of course, outgoing calls are not really the problem — any one of the above apps can rise to that challenge, and in the case of Skype, fring and Truphone, you can actually hold a conversation on the iPad itself, both using the built-in mic & speakers as well as through a set of earbuds plugged into the device. Incoming calls are only possible on Skype while the app is open, so that’s no good unless you’re expecting a call at a certain time, although Fring at least adds push notifications of incoming calls via Skype (but truthfully, they don’t work all that well). Truphone is the only app of the bunch to be iPad native at this writing, and it worked as well as the iPhone version does.

We didn’t have a Skype In number to test with, otherwise we could have routed incoming calls to the iPhone to that number and made things work a little more efficiently. However, the fact that the current iPad only works under Wi-Fi means that the minute you leave home (or a coffee shop, McDonald’s, et al), it won’t matter anyway. So as far as the iPad replacing your iPhone for actual calls, it’s a mixed bag: Just fine for outgoing in the right conditions, mostly stinks for incoming.

Message in an iPad

Next we turned our focus to instant messaging. Thankfully, AOL was front & center at launch with AIM for iPad, and since that’s our primary IM service to begin with, we signed off from our iPhone’s standard IM client, BeejiveIM, rather than cheat and install it on both devices. The day we tested was not a particularly busy one for IM’ing to begin with, but AIM for iPad did the job just fine — again, while we were within a Wi-Fi signal. We were able to access and use other IM services through Fring and Truphone, including Yahoo! and Google Talk, so those experiences were mostly unchanged from the iPhone, other than having always-on connectivity.

Text messaging is another area where the iPhone is quite capable, and not only because of AT&T’s own SMS and MMS services — there are literally tons of apps that provide cheap (or even free) SMS capabilities. Thankfully, the iPad can replicate some of that, thanks to the free, universal textPlus app. textPlus even allows you to receive push notifications while the app is closed, and you have the option of having those messages routed to your iPhone.

VoiceCentral Black Swan can also be commissioned for both incoming & outgoing SMS messages using Google Voice, but there’s no way to know if you’ve received a new SMS without actually opening the app or setting up Google Voice to forward an e-mail notification. Because Black Swan isn’t a true app created in the iPhone OS SDK, it sadly can’t access push notifications. You’re limited to only receiving such text messages while the device is within range of Wi-Fi anyway, so the iPhone keeps the advantage in this department unless you go with the e-mail notification option.

E-Mail Me Happy

Outside of phone calls and messaging, the iPad quite successfully replaced our iPhone 3GS over the course of a full day. Thanks to Apple’s MobileMe service, our e-mail was pushed to the iPad in the same way — and for whatever reason, it was actually faster at doing so! (The iPad push would chime first, followed by the iPhone a few seconds later.) Ditto for calendars, contacts and bookmarks.

Non-push e-mail accounts such as a few IMAP accounts set up on both devices were a different story. Those were fetched whenever the Mail app was actually opened, which was a little bit nerve-wracking after being used to having the PushMail app installed on our iPhone. As the name implies, PushMail uses push notifications to notify you the moment that new e-mail arrives in your inbox (it actually forwards messages from your IMAP account, which then triggers the push notification).

We cheated a bit and left the iPhone powered on in our pocket for part of the day so we could hear when PushMail was doing its job; of course, we could just as easily have installed the app on the iPad as well. But truthfully, when the iPhone was completely off, it was a refreshing change of pace not to hear the PushMail notifications going off so frequently from several different e-mail accounts.

Everybody’s Goin’ Surfin’

When it came to web browsing, there was simply no comparison: The iPad is a more pleasant experience in almost every way. It’s not just about the bigger screen, either: Having the ability to turn on the bookmarks bar so the Mobile Safari emulates its desktop counterpart is a dream come true. You also get the full website rather than switching to a mobile version by default, since the iPad’s Mobile Safari identifies itself to a website differently than the iPhone’s does — although it might be nice to have the option of accessing the mobile version by default in some cases.

Our only real quibble with the iPad’s version of Safari: It takes some getting used to going to the top of the screen in order to go forward or back a page, open a new window or add a bookmark after almost three years of having those functions at the bottom of the screen on the iPhone. Note to Apple, it might be nice to make that a little more uniform now that so many of us have both devices, don’tcha think?

One big downer is the lack of a camera on the iPad. Come on, Apple, it’s a total bummer. Once or twice during the day, we wanted to snap a quick picture or video of something, but had to remember that oops, we couldn’t — we were supposed to be living a whole day iPhone-free. While we’re sure that a camera will be implemented in the next iteration of the device, for now the iPad is an epic fail on this front. (Yeah, we know there’s even an app for that now, but it still requires an iPhone to be the eyes for it.)

Yes, Virginia, the iPad Might Replace an iPhone

In almost every other way, the iPad more than replaced the iPhone for a day. The bigger screen made watching videos, listening to music and almost every other task a complete joy, plus we had the extra incentive of watching free streaming video from the likes of ABC TV and Netflix, neither of which the iPhone does just yet. Browsing news using the iPad USA Today or New York Times Editor’s Choice apps was also a dream, as well as websites we saved later to read with the universal Instapaper Pro app. Even checking the weather was an enhanced experience, thanks to both The Weather Channel Max and Weatherbug Elite apps, both of which take advantage of the expanded real estate of the iPad to provide more impressive results.

For all of the iPad’s groovy goodness, we found ourselves missing a few of the iPhone niceties we’ve enjoyed for so long: Yes, Apple, we miss our Stocks, Clock and Calculator apps (not so much the Weather app, for the reasons noted above). Sure, there’s already several calculator apps for the iPad (most of them charging for the privilege), and even a few alarm clock or stock apps (Reuters News Pro for iPad is a free app which provides both stock quotes as well as news), but it’s just not the same experience. For instance, Apple’s Clock app can truly run in the background for alarms or the timer, where third-party apps cannot.

Aside from incoming phone calls, we only cheated once — during a trip to The UPS Store to drop off an overnight package. Since we didn’t have the excellent Trip Cubby installed on the iPad, we had to actually pull out the iPhone and log that mileage using the handset. Yeah, we could have just logged the mileage on a piece of paper to enter later, or even installed Trip Cubby on the iPad (especially since you can sync the data between devices quite easily) — but it was just easier to pull out the iPhone and get that job done on the spot. So sue us.

For all intents and purposes, it is indeed possible to replace an iPhone with an iPad, particularly if you don’t receive many phone calls (or have another way to receive calls, such as a landline or an old cell phone). The biggest dilemma for now is that the Wi-Fi dampens how much you can roam about with the iPad, a limitation we expect to see lifted when our 3G-equipped model arrives later this month and we revisit this subject again. Be sure to check back with MacLife.com when the 3G iPad ships to see how this saga plays out!