For those obsessed with financial management on the go, toting your cellphone around has become nearly as vital as having your wallet handy.

That's because so-called apps, or downloadable applications for mobile devices, can expand your phone s capabilities to include tasks typically handled on a PC. From transferring money among accounts to checking your available credit on a card to price-comparing the latest gadgets, cellphone apps add a world of financial utility. EBay (EBAY) free PayPal app for Apple (AAPL) iPhone lets you send money to friends, for example, while CheckPlease Lite (also free) calculates the appropriate restaurant tip -- and can even split the bill equitably among several diners.

App availability depends largely on the phone you use. Owners of the iPhone have the greatest choice, with access to more than 40,000 free or paid downloads in Apple s App Store -- and more than 700 of them are geared toward finance. Offerings for other devices are decidedly less plentiful. Research in Motion (RIMM) BlackBerry App World has just 26 personal finance and banking apps; Google (GOOG) Android Market offers only 24 business apps. (For the best small-biz apps for iPhone and BlackBerry, see our story here

To be sure, not all apps are necessarily worth downloading -- even if they're free. It's hard to see the helpfulness of an app that keeps track of your pocket change or lets you rate how happy you are to pay a bill.

Most apps act almost like a shortcut on your desktop PC, says Patrick Traynor of the Georgia Tech Information Security Center, which studies threats to digital information. A click on, say, the Wells Fargo (WFC) Mobile Banking App accesses the bank s web site, skipping the step of typing its URL into a phone s web browser. But, alas, you ll still need to log in. The app doesn t store any financial information on your phone, and the accounts are still password protected.

If you opt to receive texts about your bank balance or send money via mobile phone, set a PIN or password to restrict access to your device, advises Traynor. That way, if you lose it, no one can gain access, he says. In that situation, it s also important to swiftly notify your bank and change your account login and passwords, too.

Before you download an app, read store reviews from other consumers about how easy the program was to use. Most apps are built with a specific phone in mind, leading to glitches and crashes on other models or phone operating systems. It s also worth making certain that you re not paying to download an app when a comparable one exists as a free version.

SmartMoney.com surveyed the field of apps and spoke with gadget gurus to find out which free personal finance apps are worth downloading to your smartphone. Here are four standouts:

1.

Phones: iPhone. (Mint.com says versions are planned for other smartphones, including BlackBerry.)

With two 2009 Webby Awards -- one for best financial services site and another for people s choice -- Mint.com is one of the more popular online financial management tools. The free site syncs with your various accounts for a complete picture of all your finances, from, say, your checking account at the credit union to your credit-card bill at American Express (AXP) . Users can check account balances, set budgets and track spending habits. The Mint.com app, which is the eighth most popular free app out of 700-plus offerings in Apple s store, then translates the latest data into an easy-to-assess view on your phone. That lets you see if a night of fine dining will put you over budget -- or check for alerts warning you that you re within $100 of your credit card limit.

2. Bank Apps

Phones: Varies by bank.

Pretty much every bank -- including Bank of America (BAC), Chase (JPM) and USAA -- offers a mobile app to check balances, pay bills and transfer cash. Most also utilize your phone s GPS chip to locate the nearest ATMs and branches. Visit your bank s web site to see what s available.

That said, some bank apps are better than others, says Mark Asnes, chief operating officer of Wireless Zone, a wireless retail franchiser whose employees routinely download apps when setting up customers' phones. Asnes has found Citibank (C)Citi Mobile app to be particularly user-friendly. Downloading the app is easy and the interface is simple, making navigation simple even for the greenest of novices. Another plus: Citi Mobile app works well on a wide range of phones, including models from Apple, Research in Motion, LG, Motorola (MOT), Nokia (NOK), Samsung, Sony Ericsson and Sanyo (SANYY) .

3.

Phones: iPhone.

Intuit (INTU) Quicken is by far the most popular financial-management program, says Rob Enderle, president of technology advisory firm Enderle Group in San Jose, Calif. "This app serves as a natural extension for [Quicken] users; you re integrated from day one, he says. Using information from your free Quicken Online profile (which syncs with your financial accounts), the phone app forecasts your finances between paychecks, alerting you when you have a low balance or are likely to become overdrawn. But for Quicken devotees, the Quicken Online Mobile app does have some limitations: It can pull data only from the web-based Quicken program -- not the financial software installed on your desktop PC.

4.

Phones: iPhone, Palm.

Well-known financial entities like PayPal and Chase created nine of Apple s Top 10 free finance apps. The remaining program (and proud holder of ninth place) is the brainchild of tiny Catamount Software. Sole proprietor Hardy Macia says he has been perfecting this tip calculator app ever since he first developed it in 1995 for Apple s Newton PDA. He's says he regularly updates the app to incorporate the latest features that paid calculator apps offer. Users can calculate the tip in several different currencies, split the check among diners or use a sliding scale to adjust the tip total.

But there is a caveat: Whenever you re downloading a free app from a lesser-known company, figure out where they're making a profit. As for CheckPlease Lite, it generates revenue from ads displayed at the top of the device screen. You can also opt to pay 99 cents for an ad-free version.