Hi,
I have several years of advanced experience in Arduino development and 15+ years in electronics/embedded development.
I have done projects with GSM/GPRS modems both with SMS-based protocols, as well as with data connections. As a reference I normally use SIM900 shields for development.
For GSM/GPRS modules, I have used them with both hardware and software serial ports implementations with standard Arduino libraries, as well as redefining buffer sizes to accommodate for high traffic applications, among other "advanced" changes in those libraries.
Also have worked with several magnetic cards and RFID readers (with Wiegand interface mainly, but not limited to - Mag Stripe, basic clock/data can be done to) in previous projects.
Please let me know the exact type/model of your card reader (or agree to use a "generic" from ebay/china) for project development.
If you are interested in my bid, please let me know some more details about your project and I'll be able to answer you back telling if I'm up to the task or not. Feel free to contact me.
Best regards,
Carlos.