pulled calf or just cramped?

Not a cramp.

And whether it's an Achilles issue, as suggested above, or in fact a calf issue (could be the soleus muscle), do nothing that would cause it to be injured further until you see a doc.  Generally, this means nothing that causes you to forcefully lift your heel.  So no basketball, running, etc., but biking may be okay.  Swimming should be fine as well.

Keep up on the RICE (rest, ice, compression, elevation).

If it's a strain (pull, tear, etc - all the same), the doc will likely tell you to rest for 8+ weeks.  If your appointment's in 4 weeks, you'll already have those 4 in the bank.

I speak from experience.

Think I just did this last night.  1/2 way through my run workout, had already done a 10 minute warm up and 6 x 400 at 10k pace with a 1' cool down in between.  Was just getting ready to start #7 when WHAMMO the left calf, just below the bulk (most definitely the soleus) hurt like a mofo. 

So, called the wife to come pick me up (I was at the track about a mile from the house), went home, iced the bejeesus out of it, elevated it, and lightly stretched it.  Feels a little better this morning but is tender but not to the touch.  Sooooooo since I start RABGRAI on Sunday, I'm just gonna take it easy over the next few days and keep an eye on it. 

*sigh*  Hope it is back in shape for my Oly in August. 

My two cents.  I strained my right calf in May training for a 10K.  I stubbornly completed the 10K, but it took me until late June before I was able to run without pain.  

The R-I-C-E advice is the right way to go.  Basketball or anything that explosive is a no-no.  Swimming and biking are probably safer for now.  But if it hurts, quit. 

As Penn State said, the soleus is tough to stretch.  This is a pretty good set from about.com.

http://orthopedics.about.com/od/sprainstraintreatment/ss/calfstretch.htm

When I finally started running again, I did 5 minutes running with a 1 minute break to stretch and walk.  It took a lot longer than I was expecting to heal.

I'll follow up Penn State with what my doc showed me for the soleus.  Classic groc stretch is to lean aginst a wall with one leg back, heel down.  You've probably done that a thousand times.  Feels nice.  Next time you do it, after you have stretched your groc for however long you need, lower your knee towards the floor.  You can let your heel rise slightly.  You should be able to immediately notice that you have changed muscles.  As someone who never knew what the difference between your groc and your soleus was, that is a very enlightening stretch.