If you read what I wrote above, a SMART phone doesn't have a SIM card. The phone itself "contains" the number. I'm not sure what rules they apply to credit and number lapsing, but it's comparable to Digicell - credit WILL expire and the number also WILL ultimately expire. So it's no more suitable for being left unused for 9 months of the year.
Some people prefer SMART to Digicell, claiming it gives better reception and is cheaper. Maybe. My own experience with SMART was less than good and cost me a lot of money, so for the time being I'll stick with Digicell and hope they sort out their various problems.