While they are enough, you must avoid it if at all possible. Where I work, they used two pairs for the data line, and one for the phone (from the same cable)... and now every time you pick up the phone you hear data signals. If you can prevent untwisting the wires more than 1/2" you will prevent most crosstalk, and also the problem I just described.
As for the pairs: blue and white/blue are phone; orange and white/orange (one pair) with green and white/green (another pair) are data, send and receive, brown and white/brown are not used but should be terminated so they don't act as an EMI/RFI antenna.
If you look at the jack, with the pins at the top, blue (phone) will be the middle pair, and the pins to the right and left of it will be another pair (they straddle the blue pair), with the other two pairs on the far ends. The far right pair is not used, and the far left & middle (split) pair are for data.
