We did cells only until this year when we added Vonage.
Cons:
that little cell phone is pain to hold up to your ear for a long phone conversation (I swear that thing just squirted right out of my hands on a regular basis). You also can't cradle it between your face and your cheek when you have to use your hands for a second. You can use the ear bud, but then you have to go find the ear bud and untangle it. THEN, if you have speaker phone option...which is great, the problem is that it drains the battery faster. Plus people really don't like being put on speakerphone.
Cell phones feel hot against your face after a while.
When you have to charge your phone, you're trapped to speaking in this one tiny area...and taking the phone off to call and putting it back on is bad for the battery life span.
Sometimes spotty reception in the house.
Losing the cell phone in the house/car (the "lost keys" syndrome). If you have a regular phone line, you can just call your cell phone to find it, right? But you don't HAVE a phone line, and if someone else isn't in the house with their own cell phone at the moment, you can spend forever looking.
No faxing. I never realized I faxed so much, but even when it's just 5 times a year, it's a pain to have to go find a fax line that will let you fax long distance or even local.
Running out of minutes. Sure, you think you can get a jillion minutes and it will be fine...until that time you have to call the cable company and you're on hold for 45 minutes
(@#$@!!!)
Pizza delivery...no kidding, some places won't deliver if they can't pull your address up in the system through your phone number. We spent one whole year having to go pick up Dominos
The pros are that you don't have to pay for two lines. We held out for over 2 years with just using our cells, however, it was just such a pain for us after a while. Now we have Vonage for just $27/month, we decreased our cell plans, and now we break even with what we were paying for just cell service.