If you get Skype to forward calls to you over the phone network then you will pay for that too.
hi download skype get a good unlimited data plan with a good speed am using pocket wifi will last 3hrs but can use 24hrs if plug into a power outlet heres my suggestions hope it helps...
skype makes call cheap unlimited and your right skype has call forwading using your own cell number but additional payment in getting it..
here are some iphone apps you can use..
skype
yahoo msgr.
fring
nimbuzz
google talk
facetime
have you iphone jailbreak i can help you in that for free..(= and get good jailbreak apps for free sms and call to US.