IMHO it would depend on cruising area, and how you finance your liveaboard. iridium/globalsat/inmarsat provide the most expensive but best means of retaining contact with the non-cruising world. If doing your cruising on a strict budget use those funds to buy a decent EPIRB as a priority, then SSB for receipt of weather faxes and to contact with other likeminded individuals in your cruising area.
Depends if you are making long offshore passages where you may like the security of iridium phone. If you just want to communicate with others you may consider getting a wifi laptop which you can use in marinas (or outside commercial premises with permanent connections like I am doing now!)with hotspot connections - some charge, some dont. Once connected you can either e mail friends or log on to www.skype.com where you can make computer to computer phone calls anywhere in the world for free. Alternatively, you can make computer to phone calls for, currently, 1.7 cents (euro) a minute. We have family all over the world and talk to them regularly for very little cost.
In practice you spend most of your time coastal sailing with a few 2-3 week passages, so most of the time contact is easy and cheap either using local card phones or internet.
Part of the enjoyment of Ocean passages is that you are on your own, at leats it was for me. An ssb would be nice but mainly to keep in touch with other cruisers, and pick up extra weather info. You could then set it up for e-mail if you really wanted to talk to home.
better to save your money for the new sails and bits to keep you cruising in safety for longer....well thats my opinion anyway...I've only spent 2 years cruising, 12 months being the longest stretch, + 2 x 6 months
Depends upon your point of view as to what you view as essential. We now have one because we cruise in areas where phones don't exist and we still want to keep in touch with our family. I respect others that don't want this degree of connectivity but we most definitely do. Not that we use it much but it is there.
FWIW, the call charges at $1.50 a minute are comparable with mobile roaming charges. Plus there is a degree of fun to be had when calling friends from the high seas.
They haven't go round to the semaphore there yet. Incidently, you can't get a mobile signal across a fair bit of the New Forest so a sat phone is the way to go!