real time plotting on iPhone using core plot?

Yes, you can do this reasonably easily. For each received data point, append it to an array of values to display. As these data points come in, call -reloadData on the Core Plot graph (or just the particular plot) to redraw the graph, passing in the array you just added a value to in response to the -numbersForPlot:field:recordIndexRange: delegate method.

If you need to adjust the plot range to track your data points (for a moving ticker), recalculate the new CPPlotRange for the X axis and set the plot space's xRange property to that.

Use the CPTestApp-iPhone, AAPLot, or StockPlot examples as templates for how to set up the line chart overall, and modify from that starting point.

I do something similar to this on the Mac in a scientific application:
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Sounds like you could make use of a demo project I put together and wrote about here (not core plot related though).

It draws a EKG graph but should easily be modified to use another input than the repeated "heart beat"...See line 320 in EAGLView.m where the indata is entered into the array.