IOS – Why does the iPhone disconnect from wireless when it is in use

This really has nothing to do with unibody or Macs, but is rather due to physics. I'm guessing that you're cooking using a microwave oven or have it running nearby when you're using your laptop.

The 802.11b WLANs operate in the 2.4 GHz band. Unfortunately, microwave signals also fall in the same frequency band, and hence can cause interference with your wireless signal. If the interference is too high (depending on how your home is setup, how close the microwave oven is, etc.), your receiver can drop the connection.

An alternative to this would be to use a routing device that uses 802.11a. This operates at 5 GHz, which is outside the interference band and you won't notice this problem. However, the drawback is that since it's higher it frequency, it attenuates faster. This means that it will not travel as far as the 802.11b and will not penetrate through walls, etc. So if you have a big house, this might not be feasible unless if you want to set up multiple hotspots. From the linked wiki article:

Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively unused 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: the effective overall range of 802.11a is less than that of 802.11b/g.In theory, 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of 802.11b.

You can also programmatically test this. You can get your wireless details from the command line with

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

The entries corresponding to agrCtlRSSI and agrCtlNoise will give you the strength of the signal and interference respectively. Here's what a quick experiment in my house shows (explanation follows):

In the figure, you can see the change in wireless signal strength and interference as I walk from near the router (at time 0) into the room farthest away. The point to note here is that signal decreases, but noise background remains at the same level.

Then I return to the dining (next to the kitchen) and turn the microwave on for a minute (highlighted time periods). You can see how the interference increases and is higher in the next trial, when I move it to the kitchen (but not near the microwave). Note that these levels are in decibels, which means that a 3dB increase implies a doubling of interference.

The third time, I put it right next to the microwave and my laptop dropped the signal because the interference was just way too high. You can get a glimpse of how high it was, when you see it drop down to normal levels after turning the microwave off. All this while, the signal strength remained the same.

Summary: Your kitchen appliances are interfering with your signal and if you happened to be far enough from the router that your signal levels are also low, you can experience difficulties even without being that close to the appliance.

Obligatory XKCD:

'Cheater!' 'Hey, gaming on wifi? You have only yourself to blame.'

I think what you're trying to do is called tethering. There are several tethering apps available. They require your iPhone to be jailbroken though. Some apps are PdaNet, TetherMe, and MyWi. I know that with MyWi you can connect to the Wireless Network, turn off cellular data in your iPhone, and use it to tether without charges. -Notice, these apps are all Paid apps on Cydia, but if you're jailbreaking your iPhone there are ways to get the apps for free.