Step one: Be aware
150MB is enough to download the Tested Podcast three weeks in a row. Try for that last week of the month and you're looking at overages. On average, 150MB will let you load about 20 full web pages on 3G each day. Yeah, it's not a lot. If you go over, Verizon will apparently charge another $15 for another 150MB of data. So you pay $30, but only get 300MB. You want to avoid that.
Some of your habits will need to change. Your home Wi-Fi will be an oasis of data. You may, in fact, find yourself fantasizing about that spring of data while out and about. But anything to save a buck, right? Take inventory of the apps on your phone first thing. You should page through the settings to see what, if any data they are pulling down. If you don't use an app, but it likes to download updates of some sort in the background, just ditch it before you move on.
Step two: Change those settings
If you're lucky, you may find that some of your apps have the ability to download data only when on Wi-Fi. The podcast manager Doggcatcher is one such app. Aside from being a really well designed podcast app, it has a plethora of settings. In the main system settings you can check a box to only download new podcasts on Wi-Fi. The last thing you want when trying to live within 150MB of data is to find that your phone has downloaded the newest episode of a podcast over 3G, thus eating up as much as 50MB of your data allowance.
Twitter clients are also a big user of data. If you have multiple clients installed, you may actually be downloading the same updates multiple times. Make sure you turn off updates on clients you don't use frequently. If you can stand to turn them off on your main client, all the better. You can always manually refresh. Alternatively, just crank up the update interval to only ping Twitter every few hours.
If you're going to be out for a while, consider turning off your account sync. Android makes this really simple to do. The home screen Power Control widget has a button to toggle this feature on and off. You can also set this in the Accounts and Sync settings menu. Just uncheck Auto-sync; but it is easier to just use the home screen widget. Doing this means no push Gmail, contact syncing, or calendar sync. But if it's just for a little while, you can still manually sync.
If you're running a newer version of Android, you probably have the option to let apps auto-update in the background. You're going to want to uncheck that option for each app's entry. It's worth the minor inconvenience of hitting the 'Update All' button while on Wi-Fi to now blow a huge chink of your quote. Apps are getting bigger on Android, with some topping 20MB. You don't want your phone to decide to update that when you're on 3G.
One last way to use the Android system settings to reduce data consumption is also found in the Accounts and Sync menu. This is the nuclear option for reducing data consumption. If you uncheck the Background Data box, apps will not be able to use data in the background. You will only be able to initiate data sessions in foreground apps. This obviously limits the usefulness of the phone, but you can control your data completely.
Step three: Get some third party helpThere are a few apps you can use to help manage your data use. One app that is useful in this and other ways is Locale. The app will run you $10 in the Market. With this app, you can set conditions for when you area at home, and away from home. The app can automate your Wi-Fi so you can have it disabled when you're out, but automatically turn on when you get home. That way you don't accidentally forget to use your home connection instead of the mobile data. There are also plug-in in the Market that allow control of the Sync settings, so you can automate that as well based on your location or time. If you're into more tweaking, Tasker can be used in place of Locale. It's only $6.30 and it will work with Locale plug-ins.
3G Watchdog, you can watch your data usage, and even set quota alerts. The app is free and surprisingly full featured. Just go in and set your monthly quota, then set your monthly plan's start date. If you're part way through the month, you can set the counters based on what your Verizon account says. It will then track your usage each month, automatically resetting at the end of the billing cycle. The app offers helpful projections so you can see how fast you are using your allotted data as well.
In the settings, make sure you set a notification for when you have nearly reached your limit. 3G Watchdog also has a widget so you can see your usage without opening the app. With the help of apps like APNdroid or JuiceDefender, 3G Watchdog can even turn off your mobile data automatically before you reach your limit. This is a handy feature if you really want to make sure you don't get charged an overage.
Cheaper plans like Verizon's possible 150MB promotion could be a good money saver for users. 150MB isn't a lot of data by any means, but with a little planning, and some help from apps like 3G Watchdog, you could make it. Android is a data hungry operating system, so going through your apps is a must if you're going to try living on less data. It might be worth analyzing your usage over time before taking the plunge. As tiered data comes to more carriers, these tactics might be useful to more than just those looking to save by getting a cheaper plan. Let us know how much data you are using each month in the comments below!