iRule to forward

Is the connection limit imposed by IP address? If so perhaps a SNAT will work? This will translate all client request traffic into one source IP. Or is the connection limit based on TCP? If so perhaps a OneConnect profile will work. This should allow you to establish and hold a single TCP session with the pool member (SMPP service) for all client traffic. It'd be a bit trickier if the connection limit is based on application layer requests, but still possible I believe.