RN4020 data communication without MLDP

You could transfer the data over the microphone part of the microphone/headphone port present in almost all of these phones. Project HiJack provides an introduction to these methods. Most of these solutions transfer the data with Bell 202 modulation. There’s even a $79 development kit available.

It doesn’t sound like you need to actually power your equipment through the headphone jack.

You may also be familiar with the Square card reader. The older versions were passive and simply hooked up a cassette tape head to the microphone connection through a resistor, i.e. analog transfer. I believe the newer versions have a battery and a microcontroller and may also use Bell 202 or similar modulation.

As you probably know the BLE112 is a Bluetooth 4.0 single mode module, meaning it doesn't support/interoperate with Bluetooth devices older than version 4.0. The iPhone 4s and iPhone 5 are pretty much the most popular phones that have Bluetooth 4.0 support and provide APIs to use Bluetooth 4.0. Some android vendors have their own APIs such as Motrola for its Razr phone, but there is no Android API for Bluetooth 4.0. Currently any solution you make is not going to work with just any smartphone with Bluetooth.

Bluetooth 4.0 is also very different to older Bluetooths in the way it transmits and handles data. All data packets are only 20 bytes long. As you have read, at the heart of it is the slave device's (typically a sensor) GATT database which can be through of as a table with keys and values. Compared to the serial port profile (SPP) this is a very different way of thinking of data.

You can read and write the values (attributes) of the keys (attribute handles) locally (sensor / slave) or remotely (mobile phone). The idea with gatt is that instead of you writing your data like name,measurement,timestamp in one long data stream, you update the name attribute ("value"), measurement attribute and timestamp attribute in the sensor's local gatt. These changes then gets indicated to the mobile phone over the air. In short: Bluetooth 4.0 is not intended to be used for creating a data stream.

However, it is always possible to simulate or emulate streaming even when everything is packetized. Bluegiga provides a "Bluetooth Smart: Cable replacement application note" (registration required) which discusses exactly how to replace a UART cable with Bluetooth 4.0 and they give detailed explanations of how to accomplish that with the BLE112.

Update: Any device with Bluetooth and an Android version 4.3 or newer supports Bluetooth 4.0 natively. All the old vendor specific stacks have been deprecated in favor of the official support.