First of all Nokia 9210 Communicator is not a real MIDP device. The Communicator does support Java but the Java implementation is a PersonalJava implementation with JavaPhone API extension. Nokia has provided MIDP Software for Nokia 9210 Communicator that emulates MIDP environment and is mentioned only for the testing purposes.
Sockets are not supported in MIDP 1.0 specification. The only supported connection type is HTTP. Nokia's MIDP Software for Nokia 9210 Communicator is based on MIDP 1.0 specification and there is no any extra APIs.
Support for a lower-level network API such as Socket is being considered for a later version of the MIDP specification, perhaps in MIDP NG.