Calling abroad from a cell phone
Is it different than dialing internationally from a landline?
Not really. You can place an international call from your cell phone in the same way you dial from a landline: origination country exit code + destination country code + telephone number. In addition, when dialing abroad from a cell phone you can replace the exit code with the plus (+) sign. You can dial + by pressing the * button twice on some phones. Others may achieve this in a different way.
Does it cost more to dial abroad using my cell phone?
In most cases it costs much more than you would pay using a landline or even better a calling card. As an example you could pay less than 10 cents a minute using a calling card while your cell carrier would charge close to $1 per minute for the same call.