Many banks now offer official applications in smartphone and tablet app stores. In general, these apps tend to be more secure than sending information by SMS message or e-mail. Most banks go to great lengths to make sure any information sent across a network by an app is encrypted.
Make sure your bank sanctions the app before you download and install it. Most banks will include a section on their Web sites to let you know about the official app. Once you've verified the app is official, it shouldn't be difficult to download and install to your device.