Pass variable length var. between contracts. Metropolis added support for that, but solc still does not support that directly.

pass_string.sol

pragma solidity ^0.4.19;

contract One {
	string public s = "two";

     function returnString() public constant returns(string) {
          return "one"; 
     }

	function stringToBytes32(string s) constant returns(bytes32){
		bytes32 out;
		assembly {
			out := mload(add(s, 32))
	     }
		return out;
	}

     function returnStringAsBytes() public constant returns(bytes32) {
		return stringToBytes32(s);
     }
}

contract Two {
     One one = new One();

	function bytes32ToString(bytes32 x) constant returns (string) {
		bytes memory bytesString = new bytes(32);
		uint charCount = 0;
		for (uint j = 0; j < 32; j++) {
			byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
			if (char != 0) {
				bytesString[charCount] = char;
				charCount++;
			}
		}
		bytes memory bytesStringTrimmed = new bytes(charCount);
		for (j = 0; j < charCount; j++) {
			bytesStringTrimmed[j] = bytesString[j];
		}
		return string(bytesStringTrimmed);
	}

     function getString() public constant returns(string) {
          bytes32 s = one.returnStringAsBytes(); 
		string memory out = bytes32ToString(s);
		return out;
     }
}