As far as I know, no block based encryption/decryption schemes allow for bit errors to "gracefully" pass through the decryption, but I might be wrong. If any such schemes exist, they're propably quiet exotic and will create a bunch of other problems for you. Therefore, you need to do the analog transfer lossless.
This problem has luckily been solved before. The solution is a modem. And it should be one tailored to the transmission channel, meaning you can't use the same modem for both telephone and air transmission channels.
Modems are actually pretty hard to design and implement (even though they're dirt cheap), so unless you have experience in this area I would suggest to get some help :-)
Regards