We have a couple of phones in the shop that are also attached to the same line in the house.  I have a portable phone with headset hooked up to it as well as a corded phone with the dialing pad on the handset in the shop area and a wall mounted phone with speakerphone in the office.  Sometimes I cannot hear the phone ring but usually I hear it.  The wireless phone works nice if you ned to talk to someone while doing something, i.e. explaining what part you need, being mostly Norwegion I tend to talk with my hands a lot!  The corded phone, with a long cord, is nice since you can dial, recall from the handset which give you mobility.  The speakerphone in office is nice for handsfree work as well as letting all get involved in a phone call if needed.

I also have a "in-use" indicator that I bought at Radio Shack.  This red led is very bright (powered by a 9 volt power adapter) and flashes when someone is on the phone.  Makes it nice not to pick up the phone to use when someone is alread on it in the house. 

If someone answers the phone in the house and it was a call for someone else, that person will usually just call over the 2 way radio to pick up the phone.  Or be told to call on the cell phone.

I have looked at those extra loud ringers that you can buy and also strobes that will flash but for the money I have gotten by with regular phones.  I usually have people call me on my cell phone and most of the time I get reception so my phone will ring in my pocket, or they will just leave a message and my phone will tell me that.