Update: Sprint let us know that the problem is on RIM’s end, not Sprint’s. It appears users with other carriers are also affected. This specifically appears to be a problem with RIM’s BlackBerry Internet Service, so enterprise users may not be affected.
Earlier: BlackBerry email service is down for Sprint Nextel users nationwide, Peter Kafka says by Twitter. Other Twitter users seem to agree, so it might not just be Sprint.
Is your service working?