If you have a cell phone you might want to call your company to check on coverage in the various ports of call. You will find a real mixed bag of cell phone results in the messages here.
Every cell phone company has different coverage and within a given company there can be different plans, some may provide coverage while others don't. In addition, having an older phone may result in no coverage, while someone with a newer phone with the same company may get coverage.
Get a list of ports and call your cell phone provider. You may find that a small switch in plans may give your coverage in the ports you are visiting. In our case, we found that our phone was older, but they were able to send us an update via the phone, to update our phone's software so that it would work in port. My sister had the same phone, the same company, but she didn't get the update, we had service, she did not.
Cell phone is probably your cheapest method of calling home if you can get coverage. Phone cards used in port are probably next best.
Cheapest communication home from the ship is email. Ship to shore phone the most expensive.