Using a smartphone regularly can set you back $1,000 or more a year. It's so much cheaper to just use the smartphone your employer gives you. And who wants to carry around two phones anyway?

If that's your thinking, you're probably texting, tweeting, banking, browsing, emailing and posting Facebook updates on the company phone.

But by doing so, you may be giving up some control over your data and potentially a lot of privacy.

How much depends in part on your company's policy.

"An employer could give notice to the employee that the [company] will be monitoring the device, and the employee does not have a reasonable expectation of privacy," said Laurel Finch, vice president general counsel for MobileIron, a mobile device IT and security firm.

Even then, there are federal, and in some cases, state laws meant to protect your privacy and prevent unauthorized access to your stored communications or interception of private electronic communications.

But laws get broken. And even the many employers that do their best to abide by them can end up violating them inadvertently.

"Employers can always screw up. And you can sue. But why go through that?" said Joseph Lazzarotti, a partner at Jackson Lewis, a law firm that represents employers in workplace cases.

Related: OnePlus2: The best deal you'll get on a smartphone

Cynthia Sass, a lawyer who represents employees in such cases, thinks it's much better to have your own phone separate from your work phone.

Otherwise, "you may knowingly or unknowingly allow your employer to see your personal texts, emails, Internet searches, contacts, finances and any other information stored, accessed, or discussed with others on the device," Sass said.

If you're thinking "Yeah, okay, whatever," at least be aware that when you live your personal life on your work phone...

... the employer may wipe the device clean without your consent

Check your company policy. Most will indicate the employer has the right to wipe your device of all data at any time -- and they often can do it remotely, said Esteban Mata, an IT expert who has worked at Fortune 500 companies.

Most often this happens when you're terminated or leave the company, or if you report the phone lost.

So always back up everything you want to keep -- photos, videos, notes, contacts, texts, etc.

... your online searches may be seen

If your employer has installed monitoring software in your phone, it can see what sites you go to online, Mata said. It also may either block your ability to view certain sites or send a report to IT that you've accessed a site not permitted on the company's computers and laptops.

... your personal emails may be exposed

Your employer generally cannot read the emails you write on your work phone if you're using a personal email account (e.g., on Gmail or Yahoo). That's because those emails don't go through the company server.

But your employer may see those emails if it has installed a keystroke logger in your phone. That would let anyone in the IT department see what you type, including usernames and passwords to your personal accounts.

While keylogging can fall into a gray area legally, Mata said, if an employer is using one, you may not be told about it.

On the bright side, since mobile devices allow for preventative controls to be set up, employers may seek other, less intrusive ways to avoid corporate data loss, said Mike Raggo, MobileIron's director of security research.

Related: Android phones can be hacked with a simple text

Another way your employer may gain access to your personal emails: If the company is involved in a lawsuit and is ordered by the court to collect work-related emails and texts, that may include those that you sent from your own Google account. "Employers can seek a subpoena for personal email. However, the employer would need to show that the email was relevant and not unduly embarassing," MobileIron's Finch said.

Lastly, your own neglect could expose you. When you turn in your device, for example, be sure to remove all of your personal information, including that email icon that gives you (and anyone using your phone) direct access to your account.

...you should read your company policy, then ask questions

If you're not comfortable with the answers, you might just look for a good deal to buy your own phone.