In respose to Nanosecond
They do not bring cell phones with them into The Matrix. The cell phones are part of the "mental projection of their digital selves" classifing them as the same as the cell phones used by the people stuck in the Matrix. Cypher definitely left a cell phone in the Matrix when they went to see the Oracle (he dropped it in a trash can). Besides, you can't physically bring anything into the Matrix because it's a virtual world.

in response to mblase
Tank does not know who is going to be on the line when his phone rings in the Nebuchadnezzar. That's why he says "Operator" when it does.

IMO, cell phones do not have the bandwidth/error correction/reliablity/security that land lines do. The computer equivalent of cell phones vs. land lines in the Matrix are a IEEE 802.11 ethernet adapter vs. a 100 megabit full duplex NIC. Land lines (or hard lines) are also more representative of being physically 'connected' to another source. The broadcast signal of the Nebuchadnezzar is received by or connected this very source.

Also remember that only certain land-line telephones are able to get people into and out of the Matrix. People in Zion or Nebuchadnezzar-type vessels probably crack into the Matrix's version of a PBX and setup a dozen hard lines.. effectively cold-clocking COCOTs and regular phones for their own usage. ph34r!

In response to whizkid, I think you take a lot of the fun out of the movie and this node. :)