Yes, any network provider can unlock it (and especially the provider from whom you purchased it). In theory it should not be network locked but the E220 could have been distributed prior to that ruling.
Now Im confused I read widely from people that have been around that " E220 doesn't support UMTS 900"
but Cell C please fix this page because you are saying it is!!!! http://www.cellc.co.za/support/setup/speed-stick