This all depends on the antenna bands. CDMA phones, such as the iPhone for Sprint or Verizon, are harder to find carriers to use overseas, because most countries over there are still using GSM technology such as what T-Mobile and AT&T use.
No, the seasons shouldn't matter. You may need to make certain that you have no more than 9 villagers, because there are slots; otherwise, no villagers will be able to...