If I have a serviceable old iPhone 3, would I need to upgrade to 5 if I get an iPad?

If I have a serviceable old iPhone3, would I need to upgrade to 5 if I intend to get an iPad? iPhone3's limitations include its minimal access to apps. Can i get all the apps I need on iPad and use iPhone just to make calls? I can readily get sim cards for my 3 when I am overseas and cannot do that with 5.

If the only thing iPad cannot do is make and receive phone calls, and if that is all iPhone3 can do for me, would I be wiser to simply use them for separate purposes?