use strict;
use warnings;

while (<DATA>)
{
    my $SMSfield = (split(',',$_))[1];
    
    if ($SMSfield =~ /SMS[1HI]/i)
    {
       print "Match $SMSfield\n";
    }
    else
    {
       print "No Match $SMSfield\n";
    }  
}   

=prints
Match SMS1
Match SMSh
Match SMSH
Match SMSi
Match SMSI
Match SmsI  **Note this match** I think in your case, this is fine.
No Match SMSx
=cut

__DATA__
SMS,SMS1,20190811,084500,servname,servid,servname1,s1,400,300,300,300,300,300
SMS,SMSh,20190811,084500,servname,servid,servname1,s1,700,300,300,300,300,300
SMS,SMSH,20190811,084500,servname,servid,servname1,s1,600,300,300,300,300,300
SMS,SMSi,20190811,084500,servname,servid,servname1,s1,800,300,300,300,300,300
SMS,SMSI,20190811,084500,servname,servid,servname1,s1,500,300,300,300,300,300
SMS,SmsI,20190811,084500,servname,servid,servname1,s1,500,300,300,300,300,300
SMS,SMSx,20190811,084500,servname,servid,servname1,s1,500,300,300,300,300,300