Sometimes, the GeoTrust Cross Root CA is needed to get SSL certificates to work with mobile devices.
Here are the relevant webpages to study:
- GeoTrust Root Certificates
- RapidSSL Intermediate CAs
- RapidSSL and GeoTrust Certificate Not Trusted On Mobile Device (2011)
Perhaps for servers that expect visitors who use mobile devices, it may be better to use QuickSSL Premium instead of RapidSSL. Still, we will test this.