Battery management circuit for Nokia BL-4C / 5C Li-ION batteries
3rd terminal: 

The 3rd terminal on your battery is most likely to be an "on board" thermistor temperature sensor. Try this.
 Determine -ve and +ve battery terminals.
 Connect ohm meter between -ve and terminal that is not +ve.
 Blow warm air over battery (NOT TOO HOT) and determine whether resistance varies with temperature.
 Sensor could be comnnected to +ve rather than -ve but -ve connection probably most likely.

Charging:

There are many ICs available for charging LiIon cxells.
If you want to build your own Lithium Ion / LiPo charger for up to 500 mA charge rate then using the MCP83831 / MCP83832 charger IC is a very easy and economical way of doing so.
 This is eg what Sparkfun use in the LilyPad Simple.
  Data sheet here

It can literally be as simple as shown in the circuit diagram below.

. 

The resistor from Vss to Prog sets maximum charging current.
 Several other options are available by selecting variants of the basic device.   Unfortunately 3 different options are selected as a group (see datasheet page 21) providing less flexibility , but the device is still useful and well priced.
 Options include cell voltage below which charger goes into "precondition" mode,
 end point current termination level
 and i_condition / i_charge ratio. 

My main "complaint" with this IC is that the lowest voltage output level version is 4.2V and higher voltage (and very dangerous) versions are available.
 Digikey sell 3 different versions (AC, AT, DC) with the AT mainly stopping charging sooner (longer life, lower capacity), while the DC variant will try to  produce 'magic smoke' and 'vent with flame' if a very low voltage battery is charged. 

Available in stock from Digikey for $US0.68/1 and $US0.42/100.