I am thinking of getting everyone in the office SKYPE unlimiterd in/out and was curious how much bandwidth I would need in at any given time there were at least 12 employees on the phone via skype?

Will a regular Cable or mid-range DSL provide enough for that and regular internet usages like sending large emails and using our web based Customer Relationship Management Software?

You are pushing the limited. Each line will consume roughly 32kbps; with 12 employees, you are talking about 384kbps. Depending on your current network load, this is a significant load.

Depending on the supplier Cable & DSL are usually contended or shared network connectivity. Your network connection may in contention/shared with up to 50 other network connections at the local exchange. A business DSL might be 1:1, 1:5, 1:20 connection. Whilst for email and web browsing this is not a major problem it can be for Voice over IP (VOIP) applications which depend on having fairly unrestricted network access.

Usually DSL is asymetric, you might have subscribed to an 8 Meg service, but that is usually configured as up to 8MB in and 0.83 MB out from your site. The greater physical distance that you are from the telephone exchange can also reduce the advertised service speed. So in this case your 12 users would be sharing 0.8 MB with other network traffic for their outgoing voice, not allowing for rate slow down due to distance.

Skype works by digitising the voice and dividing that data into small packets of network data and transmitting that data across the Internet. Those packets of data are then reassembled into Voice at the other end. If any of those packets of data are lost or delayed on the internet you will end up with poor quality voice transmission. The worst part is that you may be hearing a good voice quality from your client, but at the same time he/she is getting a crackly poor voice content from you.